Use places that your enemy cannot get to, as in rocks ledges.
+1
Also, a high Speed/Athletics/Acrobatics allows you put distance between yourself and aggro melee types. Argonians rule at this but other races can be fast too. On a related note, I prefer enchanted clothing to armor of any kind for my archers. The goal is to be too fast to hit, making armor a hindrance.
I suggest using a bow exclusively; don't get into the habit of using any melee weapons. This will help you level up Marksman more quickly. I've heard some say that Marksman levels up plenty quickly, but it sure doesn't feel that way to me.
Obviously alchemy is your friend. A good destruction skill (and decent magicka) will help you craft some potent bows later in the game; the trade off is that you have to level destruction at the expense of Marksman. Still, if you're patient you can level both. And touch Destruction spells are better than falling back on a sword IMO. For me a "pure" archer uses no destruction, but play how you enjoy it.
Oh yes, night eye is enormously helpful for sniping in dungeons. Rings, potions, spells; I get it however I can.
I never used much crowd control with my archers, but Frenzy and turn undead (either the spell or the birthsign) may be very handy for an archer.
Good hunting!