Well, you can participate in the tournament in the abandoned factory every friday at 22:00. The best part about that is you can earn a lot of money if you win. That's not all. It can also improve your power, agility, endurance, authority and your reputation among delinquents.
Edit: You can also train your programming skills, though it would take a long time, up to the required number of programming skills so that you can find orders online for income. Better yet, if you are able to learn hacking, then you can hack the phones of many RNPCs to earn 300 credits (each from RNPCs) weekly.