From Writers Helping Writers:
DESCRIPTION: Nice guys and girls are decent, kind, morally upright, and are generally liked by everyone. They’re similar in personality to the Girl or Boy Next Door, but while the latter is often a love interest for the protagonist, nice people make great friends and allies.
FICTIONAL EXAMPLES: Samwise Gamgee (The Lord of the Rings), Beth (Little Women), Cassian (A Court of Thorns and Roses), Neville Longbottom (the Harry Potter series), Goose (Top Gun)
COMMON STRENGTHS: Affectionate, Cautious, Courageous, Easygoing, Empathetic, Friendly, Generous, Honest, Honorable, Humble, Innocent, Just, Kind, Loyal, Nurturing, Patient, Responsible, Sensible, Supportive, Trusting, Wise
COMMON WEAKNESSES: Childish, Cowardly, Foolish, Gullible, Indecisive, Inhibited, Insecure, Needy, Oversensitive, Subservient, Timid, Weak-Willed, Worrywart
ASSOCIATED ACTIONS, BEHAVIORS, AND TENDENCIES
Being a good listener
Thinking more about others than about themselves
Being protective of friends and family
Authenticity
Checking on people regularly
Being a great ally and friend
Remembering birthdays and personal events
Not always practicing good self-care (because they’re caring for others)
Being an easy mark for someone with selfish motivations
Being viewed as boring
SITUATIONS THAT WILL CHALLENGE THEM
Being betrayed by someone close to them
Being wrongly accused of unkindness, cruelty, or hypocrisy
An emergency occurring when the character is needed elsewhere
TWIST THIS TROPE WITH A CHARACTER WHO…
Is flawed and wrestles with personal demons
Has a short fuse
Is the protagonist instead of a supporting character
Has an atypical trait: Catty, Flirtatious, Jealous, Nosy, Rowdy, Scatterbrained, etc.
Link to the rest at Writers Helping Writers