You can assign a bonus to a die roll for good roleplaying of the circumstances surrounding the roll. Sometimes the roleplaying will be so good that the roll really shouldn't fail. But it's important to apply the bonus and make the roll, with the usual chance of automatic failure on the poorest die roll.

Because inevitably there are times when it'll be the other way around - applying a penalty so bad that the attempt really should fail, but you have to give the poor player a miracle chance to succeed.

Transcript

Clone Trooper: ... Clone with the Wind?
{door opens, revealing C-3PO and R2-D2}
[SFX]: kssshh...
C-3PO: See! You can do it!
R2-D2: Lamest knock knock joke ever.
C-3PO: Shh! Be encouraging.
R2-D2: This is great and all, but we need to stop the—
C-3PO: Now it's your turn!
R2-D2: Threepio, the compost—
C-3PO: You stay in here, we'll go outside and knock on the door after we've thought of a good joke.
C-3PO: I roll 12 for Bluff.
Clone Trooper: Okey-dokey!
{the droids leave the control room}
R2-D2: Okay, I see what you did there.
C-3PO: And I thought the troopers were dumb.