How long did you drop off basketball for?
I would say get to know how to get your own personal workout routine at the gym and start off there. If you were a great athlete, you probably still have 75% of what you could do. You have plenty of time though. Get your speed back, your reaction times and get back into shape. Remember aside from weight lifting, cardio (running machine, elliptical etc), sprints and jumping excerises will help you tons.
I'm assuming you know the basics of basketball? Where you ever on the school team etc? Start from what you do the best, like basic dribbling. Get two balls, do a bunch of dribbling excersises, layups, close shots. I always see people forget the fundamentals, and they are already shooting 3 pt-ers that go in 1/10 shots. The more you work on your fundamentals, the better your overall game is.
Once you start getting the hang of it, go out, play a pick-up game and get schooled. I learned from simply playing people much better than me. Learn how they position themselves when playing defence, how they are blowing past you to get to the hoop etc.
Watch a lot of college hoops (March Madness FTW

) and know how the pace of the game is and what to expect in College.
In High School, I bet you could watch some of the Senior Team practices and learn some of the plays they are doing.
I hope this will help you get back into basketball.
Josh.