Welcome-
I started with Mr. Beer, too. It was a Christmas gift back in 2002.
I made a lot of batches with it. The first few sucked, but after that, I learned enough to start making decent beer with it.
The biggest things:
1) Sanitation is key
2) DO NOT top off with tap water. Always get the chlorine out first.
3) Booster is a joke. I hope they got rid of it by now. If not, just substitute plain unhopped DME for it. You will thank yourself.
4) give the yeast time to work. Don't be in too much of a rush. brew enough to have a backlog, so that you are not tempted to drink them prematurely.
Good Luck! Keep asking questions and you will get all the answers you need here.
Steve