If there is one piece of advice that I can offer anyone learning a second language, it is to be very, very familiar with the grammatical concepts of their own language. Know what all those odd cases are and have some clue what the terminologies mean.

I was at a complete loss about what vocative and genetive meant when they popped up in my textbook -- and I've got a background in literature and written English.

Here's a quick idea of what they are:

nominative	the boy is here
accusative	I see the boy
genetive	the boy's coat
dative	to the boys
vocative	com here, boy!