I can agree with what Eske said.
I've killed off 90% of dungeon trash and dungeon bosses I've faced this way, including dragon priests -- Snipe, break LOS from the original firing spot, repeat. You just have to be patient. If they heal themselves? Great, gave you more time to plunk in one or two more arrows and more chances to skill up Archery. The ones I didn't kill this way were the ones from early on before I figured out how to snipe effectively or much later on when I was heavily skilling up Destruction.
I just started a new character to mess around a few days ago and have had a chance to figure out a few tidbits that are handy when playing a sneaky range build. For starters, you can "activate" torches on walls to put them out (you actually take them into your inventory but you can just drop them and they're no longer lit.) This can help with setting yourself up with a space with less light than normal since lighting influences how well enemies can detect you.
Also, if your sneak skill is high enough you don't have to LoS your firing spot...you just have to move far enough away from it that your enemies don't detect you when they run to where you were when you fired.
I mentioned this a bit earlier in the thread, but it bears repeating...you can distract enemies by firing at a spot behind them relative to where you're standing. They'll go to investigate where the arrow impacted which can help you create a larger gap and potentially get an extra shot in before you have to relocate.
Another sneaky trick that would classify more as an exploit than anything else is a way to level your archery to 50 fairly quickly/easily. In Riverwood is an elven dude named Laethal who is part of a quest. If you chose to finish the quest in a way that favors him, you can have him join you as a companion. Not only is this handy for early storage before you've picked up your first house, he's also an archery trainer. The trick lies in the fact that when he's your companion, you have direct access to his inventory. Pay him to train your archery and then tell him you want to store something with him. Take your gold back. Repeat. You can train 5 points to archery right away, and then every time you level up you can train 5 more points up to a maximum of 50.