you should pick up a copy of 'How to rap-the art and science of the hip hop mc' by paul edwards. Really think it will help you. Also probably the most important thing is to be yourself. Don't rap about things that aren't true, the subject matter seemed completly disingenuous. If you haven't grown up in the ghetto or own expensive cars then don't pretend you do, instead rap about something that is actually true. A far more interesting song would be about your aspirations for these material things.
Hope this helps.
