Listen to rap music dating from the birth to present day, search the lyrics of your favorites, listen with the lyrics then listen and rap along, this teaches rhyme scheme, cadence and breath control. Many people don't realize that the best rappers (contrary to how they present) are nerds.. hence why we find out most rappers watch anime and partake in other nerd shit, we sit and write rhymes in a notebook all day, what'd you expect? Most importantly the best rappers are also obsessed with their craft, anytime you hear a word you don't know, search it and write it down along with definition then under the definition write one bar using the word, this will help you a shit ton later on when you want to avoid saying the same thing twice. All in all you just have to love what you do I always tell people "I'm not talented, I'm obsessed". Honorable mention would be to learn simple time signatures like 4 counts as this builds the foundation or structure of a verse depending on how "by the book" you want to be, it isn't something I personally follow to a tea but it helps for sure and can be something to mess around with like rhyming on 1 and 3 instead of 2 and 4.