Rolling randomly. I don't know who said this, but it's a good rule of thumb:
"If your answer is not "yes", roll a die". (Or something like that).
I do quite often roll randomly without game rules. I simply roll a die, higher the result, better outcome for character's point of view. These are the situations where character's characteristics have nothing to do with the actual outcome of roll.
For example, if character is trying to charm someone, roll is based on her skills versus difficulty based on the other being charmed. That situation can be played according to game rules.
But when there is something I don't want to just decide, I let a die make a decision for me. Player might ask, are there guards at that corridor watching the air vent she's hiding in. I don't have to roll do guards spot character, as they aren't necessarily searching her at the moment. I let the die decide. Rolling D6 I get result 5 or 6 no, no one is watching at the air vent at the moment. Rolls 1-2 yes, most definately.
Also you can determine "shit hits the fan" effect with random die roll.
Text from Code/X (download free here: http://www.burgergames.com/codex/)
Sometimes it is impossible to decide if and how the
characters could affect the situation and it all boils
down to luck. In that case, player or Gamemaster rolls
a single die, the lower the result, the worse the situation. Rolling 1 means something exceptionally bad and
rolling 6 some kind of an unexpected benefit.
For example, the character fires off a long burst in a laboratory, instantly reducing test tubes, pipes, contains, jars and whatnot into fragments, trash and shreds. Is there a fire? Is there a dangerous chemical reaction? Will he get splashed by the zombie enzyme?
The gamemaster rolls 1D and result is 2. Not good. Multicoloured puddles on the floor begin to boil and suddenly the air above them bursts
into green-blue flames. Characters would do wisely to get out as soon
as possible. On a roll of 1 there could have been an explosion, or the
shooting character would have been sprayed with acid.
On a roll of six, he would have been sprayed with a mysterious chemical that heals his injuries, or a whole bunch of enemies would have
gone up in flames.