From the Dungeons & Dragons Player’s Handbook (2014, ISBN-10: 0786965606, ISBN-13: 978-0786965601), page 125:
If you have inspiration, you can expend it when you make an attack roll, saving throw, or ability check. Spending your inspiration gives you advantage on that roll.
Additionally, if you have inspiration, you can reward another player for good roleplaying, clever thinking, or simply doing something exciting in the game. When another player character does something that really contributes to the story in a fun and interesting way, you can give up your inspiration to give that character inspiration.
Current House Rule
The PHB listings for Ideals, Bonds and Flaws are a bit loose to interpret in gameplay. The following rules provide a more concrete set of guidelines for characters to earn inspiration through gameplay rather than just DM fiat.
IDEAL: What gives you purpose… (pick one)
* VENGEANCE: Someone you loved was killed one of the following types of creatures: Aberration, Dragon, Elemental, Fiend, Monstrosity or Undead. Whenever you reduce a creature of that type to 0 hit points, you gain inspiration.
* CHEATING DEATH: You are dangerous thrill-seeker. Whenever you are reduced to 0 hit points but then recover, you gain inspiration.
* PRESERVER OF LIFE: Whenever you restore a living creature with 0 hit points back to 1 hit point or more, you gain inspiration. (Beasts, dragons, giants, humanoids and monstrosities count as “living creatures.”)
BOND: Love and hate… (pick one)
* FELLOWSHIP: Name a close relationship you have with another character in the party (sibling, parent, child, spouse, lover, friend since childhood, mentor, personal idol, owe a life debt, both named in a prophecy). Whenever you spend a long rest within 30 feet of this other character, you gain inspiration.
* ENEMY: There is one NPC out there who wants you personally to suffer, maybe wants you dead. After a long rest, the first time you come within 30 feet of that NPC or members of that NPC’s organization, family or henchmen, you gain inspiration.
FLAW: Your weak spot… (pick one)
* IMPAIRED BODY: You have a minor physical limitation that occasionally hinders you (bad leg, missing fingers, weak heart). Whenever the DM has your character make a Strength, Dexterity or Constitution saving throw, you may choose to make it with disadvantage (citing your Flaw), after which you gain inspiration.
* IMPAIRED MIND: You have a minor mental limitation that occasionally hinders you (addiction, hearing voices, overconfidence). Whenever the DM has your character make an Intelligence, Wisdom or Charisma saving throw, you may choose to make it with disadvantage (citing your Flaw), after which you gain inspiration.
* CREATURE PHOBIA: You are terrified by one of the following types of creatures: Aberration, Dragon, Elemental, Fiend, Monstrosity or Undead. After a long rest, the first time you come within 30 feet of any creature of that type, you immediately suffer the Frightened condition for one round. (A frightened creature has disadvantage on Ability Checks and Attack rolls while the source of its fear is within line of sight, and you can’t willingly move closer to the source of your fear.) At the start of your next turn, you are no longer frightened and you gain inspiration. For role-playing, this Flaw may also lead to intolerance toward the creature type, or a tragic backstory involving loss or captivity by such creatures.
* DAMAGE PHOBIA: You were traumatized by suffering horrific injury from one of the following types of damage: Fire, Lightning, Necrotic, Poison or Psychic. After a long rest, the first time you take damage of that type, you immediately suffer the Frightened condition for one round focused on the source of that damage. (A frightened creature has disadvantage on Ability Checks and Attack rolls while the source of its fear is within line of sight, and you can’t willingly move closer to the source of your fear.) At the start of your next turn, you are no longer frightened and you gain inspiration. For role-playing, this Flaw may also lead to fear of ordinary flames like campfires (fire), fear of thunderstorms (lightning), a weird habit about making sure food is “clean” of contamination (necrotic or poison), or nightmares about something awful stalking your dreams (psychic).
Previous House Rules…
House Rule #1: You may decide to spend inspiration after seeing the results of the first d20 roll. (In other words, you choose to get advantage only if you need it.)
House Rule #2: Each Ideal, Bond or Flaw can trigger the Inspiration benefit once per day. If a character already has Inspiration, this benefit does not stack – that is, a character can only gain the bonus once at a time.
IDEAL
What event best illustrates the core motivation you have to go adventuring? Once per day when you perform this task, you gain Inspiration.
Example possibilities…
I draw strength from my fighting spirit. Whenever I deliver the killing blow to any foe more powerful than me (a creature whose challenge rating exceeds my character level), I gain Inspiration.
I draw strength from my belief in the sanctity of life. Whenever I save a dying creature (not just stabilize but restore health to a target at 0 hit points), I gain Inspiration.
I draw strength from my arcane curiosity. Whenever I learn a new spell or use a spell scroll for a spell I’ve never cast before, I gain Inspiration.
I draw strength from my faith in the divine. Whenever I spend a full day in service labor performing sacred rites, I gain Inspiration.
I draw strength from the love of my audience. Whenever I spend a 4 hours or more in a day performing for a public crowd, I gain Inspiration.
I draw strength from my people’s survival. Whenever I spend a full day hunting or building shelters with 10 or more individuals from my native tribe, I gain Inspiration.
I draw strength from my greed. The first time each day when I steal someone else’s treasure (object’s value worth more than my level x 100 gp), I gain Inspiration.
I draw strength from my duty delivering justice and protecting law and order. Whenever I imprison a lawless individual (a chaotic character equal to or greater than your level) or return stolen property (worth 100 g.p. or more) to its rightful owner, I gain Inspiration.
I draw strength from my love of anarchy and freedom from tyranny. Whenever I free an imprisoned person who shares my love of liberty (a chaotic character equal to or greater than your level), I gain Inspiration.
I draw strength from my hatred toward aberrations, alien creatures born outside our universe. Whenever I deliver the killing blow to a creature of such dreaded type (reduce it to 0 hit points), I gain Inspiration.
I draw strength from my hatred toward celestials, supposedly holy creatures in service to the divine. Whenever I deliver the killing blow to a creature of such dreaded type (reduce it to 0 hit points), I gain Inspiration.
I draw strength from my hatred toward dragons, scaly flying engines of death and destruction. Whenever I deliver the killing blow to a creature of such dreaded type (reduce it to 0 hit points), I gain Inspiration.
I draw strength from my hatred toward the fey, immoral tricksters that steal children and mock divine order. Whenever I deliver the killing blow to a creature of such dreaded type (reduce it to 0 hit points), I gain Inspiration.
I draw strength from my hatred toward fiends, demons and devils that only exist to corrupt and destroy innocence. Whenever I deliver the killing blow to a creature of such dreaded type (reduce it to 0 hit points), I gain Inspiration.
I draw strength from my hatred toward giants, descendents of primordial elemental horrors that once fought the divine order. Whenever I deliver the killing blow to a creature of such dreaded type (reduce it to 0 hit points), I gain Inspiration.
I draw strength from my hatred toward monstrosities, savage creatures mutated by magic or some other unnatural act of miscreation. Whenever I deliver the killing blow to a creature of such dreaded type (reduce it to 0 hit points), I gain Inspiration.
I draw strength from my hatred toward undead, corpses and spirits whose undying hunger for the spark of life makes them all horrid predators. Whenever I deliver the killing blow to a creature of such dreaded type (reduce it to 0 hit points), I gain Inspiration.
BOND
Who in your adventuring party is the focus of your deepest personal connection? Whenever you spend a long rest in the company of this person, you gain Inspiration.
(When playing with new friends, use “the character of the player on your right” for your bond.)
Example possibilities…
I share a close connection with (_______), as we were both ordered to look out for each other by some personal authority (military order, church, or just dying wish of respected common friend).
I share a close connection with (_______), my beloved (husand and wife, secret or open lover).
I share a close connection with (_______), who shares a common hatred (both lost a loved one who was killed by the same villain).
I share a close connection with (_______), my professional master or student (if one character higher level than another).
I share a close connection with (_______), my professional rival. I live to perform better than this character, either out of respect or competition, but I also support his or her winning “second place” behind me.
I share a close connection with (_______), the subject of a biographical work I am working on. I live to document and tell stories about this character’s life, either celebrating victories or mocking failures.
I share a close connection with (_______), a fellow conspirator. We both secretly work for an NPC no other characters know about, sharing back detailed information about adventures, travels, encounters and discoveries.
I share a close connection with (_______), part of a debt of honor. I have pledged to my king, master or church to accompany, protect and support this other character, even giving my life to such a promise if need be.
I share a close connection with (_______), part of a debt of shame. I once disgraced or wronged this other character and adventure with them out of a sense of duty to make good on my past misdeed.
I share a close connection with (_______), the subject to my sworn evangelism. I follow this character everywhere in hopes of converting him or her to my religious faith or political allegiance.
FLAW
What personal problem most often causes you to fail during stressful moments? Because of this flaw, once per day you may choose to suffer disadvantage on an attack roll or saving throw when you otherwise would make a normal roll, after which you gain Inspiration.
Example possibilities…
I suffer a minor crippling injury from long ago that can never heal correctly.
I suffer from an addiction to something that impairs my senses and mind when I take too much, and also causes me withdrawal when I don’t get enough.
My sense of overconfidence makes me sloppy in combat or opens me up to dangers I could otherwise easily avoid.
I suffer a pathological fear about becoming injured (traumatophobia), sometimes making me flinch while in combat or freeze up in danger.
An ill fate or destiny foretold at my birth by oracles continues to make itself shown, causing me to fail during moments of crisis.
An ongoing curse placed upon me by an old enemy afflicts me from time to time.
I suffer visions and voices from things no one else sees or hears. I don’t know if these are hallucinations caused by madness or actually my own personal haunting by real spirits.
I have a tricky faerie guardian spirit who needfully wants me to depend on it rather than act independently under my own will.
I am tormented by a corrupting entity that needfully wants me to depend on it rather than act independently under my own will.