Here's a great (albeit cheap) way to gain lots of experience. Before you do anything that's going to net you some experience (such as picking locks, hacking, et cetera), change the game's difficulty setting to Very Hard. Then, hack the computer or pick the lock (or whatever). Successfully doing so on a harder difficulty level will get you more experience. You can also utilize this technique on mortally-wounded enemies to gain more experience from them as well. Just be sure to change the difficulty back to a more manageable level when you're done!