I think I did that as a thief archer. Unlike Matty, I never actually ran away from any fights. If it was too difficult, I just retried it, over and over again until I worked out how to win. But as an archer, that's rather easy. Basically the strategy was, shoot an arrow-->run back-->repeat. The other strategy was to just find someplace that the AI couldn't reach me and pummel them with arrows from there. But even with strategy's like those there are still fights that actually prove really difficult and can take 30mins-1hr to win. For me this was due to lack of 'retreating' space, nothing to jump on or high level ranged opponents.
I remember 1 fight against a frost necromancer boss and a couple of spectral shades that probably took ~50 attempts. The shades would 2 shot me (in melee), and the necromancer would use a ridiculously OP frost spell which would slow me so much that i couldn't dodge the second one, which also happened to be the killing one. I couldn't kill the shades or necromancer with sneak archery attacks (even with poisons) so I ended up using a combination of my best buff potions, archery (to initiate the fight) and dual wielding poisoned swords while unleashing shouts with my companion tanking the shades as I continually staggered the necromancer after I Fus'Ro'Dah'ed him into a corner. I had a pretty good feeling when I eventually won.
Also Dragons are pretty easy, just hide behind a rock or tree when they flame you and pummel them with arrows.