In my games, I have few ironclad rules that I run by. Generally, I only have one that encompasses everything I’ve learned about running games. I post this here because it shapes and forms everything I create for my games.
The Rule of Cool
If a player comes up with something cool, let them do it! Ask for rolls, let them roleplay it out; let them enjoy being their character, rather than just playing a game. Do this often enough, and try to stick to the rules when doing so, and your players will help you run the game, making your life easier. This means learning the heart of this rule: Never Say No.
If a player comes up with something that could be awesome, say, “Yes, but roll this to see if someone notices you.” Keep it fluid and be able to improvise. This is where preparation comes in; you have to be prepared enough to improvise a reaction to the character’s actions. This is where Dungeon Master’s Guides and similar documents come in; hopefully, if the creator hasn’t been stupid, they’ve got advice on how to handle things like this–for example, knowing the averages for ability scores, to-hit rolls, average damage, etc, and using those to make the player’s actions have meaning when they take them.
This is why I love DM Screens, and I hate that 5e’s won’t be out until March 2015.