I found the most useful tool for picking locks is using the various marks on the lock graphic to line up my pick. Once you get the lock to move, it's only a matter of figuring out which way and how far to go.
Excellent advice, especially if you're playing on an HD set. By making careful note of the subtle variances in the texture map around the lock, and using them as a reference for the "o'clock" position of your pick, you can really save yourself a lot of breakages. If you break a pick, you can use a new one, and start very close to the correct position.
Other tips (I'm playing on a console, so PC players may have a different experience):
1) Move VERY slowly. It's not a race.
2) Use a light touch on the right thumb stick. The anolog sticks are very sensitive, and you can move them with extreme care.
3) The moment you start to feel resistance, don't "walk" the stick back to the neutral position.
Immediately let it go. It will return "home" on its own. This will save a lot of accidental breakage.
4) Always buy/loot available picks. You always seem to run out at crucial moments, otherwise.
5) Thoroughly search downed NPC's. A fairly good deal of the time, they'll be carrying keys that will open chests or doors in the area, thereby preserving your picks.
6) Keep your eyes on the triangle-shaped hashmarks on the left of the lock graphic as the butt of your dagger moves upward. These are very handy
de facto gradient markers, and help immensely to gauge whether you're moving closer, or farther from the sweet spot, letting you adjust accordingly. You'll always feel/hear the lock disengage just as the dagger-butt eclipses the inward-pointing corner on the second marker from the top.
7) Unless you're desperately low on picks, always take the time to at least try high-level locks. Nothing bumps your lockpick level faster than having a relatively low skill, but successfully picking an Expert or Master-level lock. It can be EXTREMELY tough, but in a very technical sense, any lock is pickable by any level character (except, of course for those that expressly state that a key is needed). You just have to take your time, and be extremely careful. Even if you fail, you still get a slight bump just for trying it. Practice makes perfect!
Good luck!