*Laughs*
You jump right in and ask the hard ones don't you? It does depend to a large degree on your own musical ear, and your ability to pick out what makes a particular kind of music a "style"...but what you might want to try is start with a piece of music that you wrote in one style and try to add elements of a different style to it.
For example: (Let's take three totally different styles.)
Let's say you write trance...dancing, day-glo, hoovers, the works! Take your trance music, and try dropping out most of the rhythm parts. Just nix the track entirely. Ok, now try putting the rhythm parts back in, but only use sounds that you'd find in an orchestra. Timpani, gongs, field snares. Consider slowing the tempo down a bit.
With me to far? Now you've got yourself, some marching-trance.
Now why not try adding some Surf-style guitar lines? Maybe grab some samples (legally) from old Beach-boys tunes. See if you can make those fit.
There you have it! Orchestral-Surf-Trance! Sure it may sound silly, and some combinations won't work, but you'll learn a lot about mixing styles.
Good luck!