here is a metaphor i used at one time....
"I'm lappin muthafuckas around this mothafuckin gangsta track"
i was talking about how, if it were a race, i would be so many steps ahead of them, i would be lapping their ass around the track. also, i was talking about how many steps i was ahead of them in the game with the actual track i was rapping on.
to some people, it just comes out naturally. i use metaphors quite a bit, and honestly i dont' really think it out, when i am writing that shit down as soon as it comes to me head, i realize alot of the time after the fact that it is a metaphor.
the best advice i can give you is: don't try and be like someone else. it definately helps to have a larger vocab. i failed english class 2 years in a row, and barely passed my sophmore year....but i still have a very good vocabulary. i don't read books either, so i dont' have any tips really on how to boost your shit up. maybe look at a thesaurus, and a dictionary to not only know what the word means, which is very important, but also another word that means the same thing. but don't only use big words and shit, cause that is annoying. you have to wrap it altogether. make your shit interesting. don't use the shit that has been used a million times. i know once i hear something that i have heard a million times, like twice in one song from a guy on his cd, i'll skip the song or just turn it off. also, your delivery is another way to keep peoples attention. and yes, practice makes damn near perfect.