Choose whether you want to train guards or train big men. It's mostly a personal preference decision, though it maybe more expensive to guy decent guards, so training them can be beneficial.
Then, buy some trainees. I would suggest 18 or 19 year olds with at least 6 potential, and with 50-55 total skills points (no including free throw, stamina and experience). For guards, be cautious about low OD, and PA (and jump range), as training those is somewhat slower than training Jump shot, handling, driving. For bigs, watch out for low inside shot and inside defense, and rebounding.
For the positions you are not training, you can get some older, veteran players, with salaries in the range of $7-10K. Above that and you're just wasting money, as well built players in this salary range should be good in initial divisions. If you can't get any decently priced veterans like this now, I would wait until after the deadline for transfers for the playoffs comes (near the end of the season). At that point, prices tend to fall, and you can pick up guys cheaper for the next season at that point.
Then, expand your arena. Mostly bleachers at first, but every so often expand some of the lower tier and a few courtside. But stick with bleachers initially.
Then, read the guide and the FAQs, and ask questions. It's a good community of people here who are happy to help out.