Obviously food - adequate protein and nutrient balance. Nothing crazy here, it's not rocket science you don't have to run your diet like a monk.
Training, a program that concentrates on good exercises that translate well to performance and fundemental strength. Squats, deads, powerclean, bench, row, standing military or push press, chins. All free weight, barbell, no machines. Work at getting better at them.
Probably the best descriptions on squat, bench, and dead on the net here. Read and study them carefully no matter what you think you might know.
http://www.midwestbarbell.com/totalelite/index.php?showtopic=14
This is a pretty fundemental basic program used to strengthen and add muscle to athletes. If you want to gain weight, eat more, if not then don't. You will get strong regardless but obviously stronger if you keep eating to put on more muscle. It's pretty bullet proof and will work quite a bit better than 99% of the garbage that's out there. Variations of it have been used extensively anywhere from novices to elite athletes over the years. It pretty much works and the guy who made it, Bill Starr is about the best strength coach to have walked the earth.
http://www.elitefitness.com/forum/showpost.php?p=4497774&postcount=15
If you have $25, buy Rippetoe's Starting Strength. It covers the exercises and programing for novices in depth. It's written from a coach's standpoint so it should get you up to speed. It also includes the powerclean which alone is worth purchasing the book since you are serious about sports and most high school coaches can't teach the lift worth crap (let him read the book after you). Probably the best money you could spend if you want to get strong. Rippetoe uses very similar programs to the one above and is well known for his success at strengthening and adding muscle to novices in very short time frames.
www.startingstrength.com