Hip Hop is created largely from samples. You need to have a great record collection and know every record. Sometimes you will take a sample and you just can't make it work. Don't worry, you took a chance and failed. Next time you'll take a chance and succeed.
Some people are too scared to take chances.
You need to be able to make rhythms out of sounds that no-one has thought of making rhythms out of, well almost. Hip Hop used standard drum sounds in the past, but these days you have to go far, far beyond that. Don't forget that for many people Hip Hop and Rap are two sides of the same coin. You need to know what distinguishes a good rapper from someone who would be better off staying on his street corner. You need to respect the laws of copyright.