let me say something about the straight letter thing. when people told me that i was like what the fuck are you talking about jackass. now i get it, cus thats how it works.
do straight letters to practice keeping the width of the letters all the same. go practice UNDER A BRIDGE with paint, its not like drawing with a pencil. just dont go over anybody that looks like they are good. once you can do basic letterforms good, keeping the width and size of your letters the same, and you understand what exactly makes up a letter, you can THEN reinvent letterforms to suit your style. it will help tremendously when you try to paint your first peice or try to come up with a throwie.