well, getting better at sports isn't an overnight thing, unless you use rhoids, but, seriously, don't use steroids.
you gotta practice the sport itself a lot and make a commitement to practicing the sport. try hard in practice, and do off-season camps.
go to the gym three times a week to lift, taking a day off in between the days you lift so your muscles can rest and develop. everything you do at the gym you should do three sets of 8-12 reps. you know its enough weight if you can just barely do the last rep.
lastly, make sure you do cardio at least twenty minutes a day. that is running, jumping jacks, etc. anything making your heart pump and you breathe heavily. just doing the sport should give you more than twenty minutes of excellent cardio.
and of course, cut out all the fatty foods and alcohol. but that's a given.
and don't smoke weed. you'll get mad munchies.