!st off let me say, I am using a modded version of Skyrim with increased weapons damage and on Master so NPC aim is a bit better and a whole lot more deadly, as 1 arrow is more than sufficient to kill me. That being said, the principles are same and should apply equally to Vanilla unless you're getting shot in the feet alot.
Some people say that when facing deadly archers, sneaking while blocking is the best bet because it covers more of your body. While sneaking to get more cover out a rock formation is usually a good idea, I have noticed that sneaking spreads out your body horizontally and exposed your flanks to attack while blocking with a shield. This makes it difficult to protect both you head and sides simultaneously. Since there isn't yet any location based damage, getting hit the elbow can be just as deadly as getting hit in the eye. Also archers tend to aim above the waist, mostly at your upper chest, head, and arms. What I have found is that if you stand upright, and walk towards the enemy archer while keeping him/her just a smidge to the upper-right of your targeting recticle, then you will block 95% of arrows headed from that particular archer. Of course this only works against a single archer, so if you've got the diffuclty ramped up high and can't survive more than a single hit (if that), you're better off dodging, looking for cover, and then going with a ranged attack when handling mutliple archers.
Generally dodging is superior to Blocking if you've good reflexes and/or any of the time slow perks/shouts. But in that short range distance when you're closing in on them, blocking is usually the winners choice.
Good luck out there, and keep those damnable arrows away from your knees!!!!

