Hmm... training tactics is obviously important, but if I were you I'd certainly give Richard Reti's "Masters of the chess board" a read. I hope I would have read that book much earlier, I was maybe rated around 2000 when I read it and I think reading it still helped me tremendously. Trying to remember opening lines makes no sense IMO but Reti teaches you how to understand the opening phase, so you can make better decisions in unknown opening positions (so most of the opening positions at this stage). I cant recommend that book highly enough, it's one of the best chess books I've ever read and I think it should be fairly accessible for beginners. I doesnt go over basic mating patterns (checkmating patterns!) or how the pieves move of course, but I think you are already familiar with those.
Not sure if that's the best piece of advice you'll get for that match against your friend, but reading that book will help you become a better chess player in the long run for sure (if that's what you are after
).
edit. Reti's idea is counting one point for each move with one of the two central pawns, developing a knight or a bishop and for castling. The one who has more points is usually doing better. And making a move with one of the central pawns, bringing out a piece or castling is almost universally good during the opening phase of a chess game. And say you are up 2-3 points, it usually means you have initiative and should start attacking your opponent. A lead in development isn't a static advantage, because if you end up not using it to your advantage (attacking your unprepared opponent), he usually catches up to you. He also explains concepts like gambit, initiative, development, weak squares etc. really well.
Last edited by JekkuNaama; 03-23-2014 at 06:14 PM.