If you mean "gaps in my education" or "basic things that I don't quite understand", you could try studying some high-quality texts. Look for books written by extremely smart people who are trying to explain the ideas rather than taking you through the standard topics. Hamming's books on probability and signal processing and Strang's books on linear algebra and applied math come to mind.

Alternatively if you're really interested in intuition, you could also look at the Math Olympiads. Pick a problem, beat your head on it, finally look at the solution, repeat. There are web sites and prep books.