Every GM has her own tools of the trade, little tricks she uses in his games. Sometimes you can just shake things out of your sleeve, but sometimes it's good to have some kind of tool you can use when in doubt. A tool I've used for years is a Luck roll, a simple d6 you roll for the character or group doing something.
If the result is 6, the character is really lucky and benefits from the situation greatly - a scout sees the enemy general halting a support wagon and giving it strict orders which reveal location of a secret base.
If the result is 1, everything goes as badly as it can. And even worse. The character sneaking around gets lost, strains his ankle, and encounters a hostile patrol - lead by the villain's general.
5 means luck, 2 complications and 3-4 that nothing special happens or an event that takes place is neutral, and can lead to good or bad.
This method can be changed easily, for example Savage Worlds hindrance unlucky can give -1 modifier to the die while lucky or very lucky gives +1/+2. If you use this technique often, you might want to replace the normal benefit/penalty of the flaw/edges with this.
Do you have similar simple techniques you use in your games?