Jesse Schell (in The Art of Game Design) has done excellent work defining a taxonomy of game mechanics. Each game mechanic you can think about almost certainly falls into one of the following categories:
- Space
- Objects, Attributes, and States
- Actions
- Rules
- Skill
- Chance
By understanding these categories, you will be able to have a clear idea of how to collocate your new game mechanic and therefore deliver a more conscious design.