When you master PvE, your next step is getting to PvP asap:
Hinkley. I suggest everyone to have at least 1 character there and pvp for about hour per day. First of all - it's fun if not playing too much, it can be nice relax from pve braindeath.
More important - it gives a lot of general combat experience needed to every player - how to hide from enemy fire, how to heal effectively, how to manage using of AP points in pvp, how to maintain your range. You can't become superpro with this, but average and even above average infantry - maybe.