You're not alone Zombra, I consider myself reasonably accurate with my bow at long range vs. static targets, need to get a bit closer for moving (depending on how fast they're moving) but still manage to hit my target however I too have trouble hitting dragons. I was attacked by one in the Reach near a tower (can't remember the name) that leads into a Forsworn camp (but the door is locked from the inside) where that
is located. It was circling overhead and it followed a sort of predictable path where it would circle overhead, fly out and then fly low and fast over me as if to strafe me (it never did). I aimed at the largest portion of seen mass (i.e. it's chest and head as it was flying towards me) and loosed off an arrow and I swear it looked like I got it in the neck but apparently I missed. And don't even try to shoot a dragon that is circling overhead, they have a unique ability to turn away from their projected flight path just as you loose an arrow.
Which is why I summon my Flame Atronach when it's time to fight a Dragon. They seem to hit all the time and they have almost impossible lead angles, like 90 degrees, as I saw her shoot once. I actually stopped worrying about the dragon to watch what she was shooting at (thinking there was another, more important enemy or a second dragon) and while I watched the fireballs speed off into no where, the dragon flew into them... (Perhaps Flame Atronachs have unbeknownst pre-cognitive abilities?) The guards feature the same ability with their bows. Dragons don't seem to land unless they get hit, so having the Flame Atronach cast fireballs at it causes it to hover and/or land. During this hovering stage arrows seem to hit and, of course, arrows hit when the dragon is on the ground. For now friend, I recommend you get youself enough magical competence to summon a Flame Atronach to take care of the moving ranged attacks while you focus on the static. My "non-magic" warrior suffers from this greatly, so now he too has had to dedicate a few levels to upgrading magicka.
Also, just be careful (if you're attacked by a dragon near a small town such as Riverwood) if you decide to run back to the town for the support of archers. I was going to clear out Embershard mine (to start my Smithing leveling) when I was attacked by a Dragon. Being clearly out matched alone, I had to head back to the relative safety of Riverwood dodging blasts of ice breath as I ran/sprinted back. I had killed Mirmulnir (or whatever the first dragon's name is) and the Jarl had placed soldiers in Riverwood so they were able to shoot the dragon with their bows. It landed (rather heavily it seemed, but it didn't slide like they do when they've suffered enough damage) in the clearing near the Saw Mill and I was sprinting there to attack it when Gerdur decided she wanted a piece of the action and ran in with a dagger and wearing only her dress. I watched in confused disbelief as she took a few swipes at it before it promptly snapped at her killing her instantly. Also, poor old Stump the dog was a casualty as well. It's nothing major, I guess, in the long run but now poor old Ralof has lost his sister, Hod has lost his wife and the kids don't have a mother. Though none of them seem to realise she's gone. I can see the tombstone now: "Gerdur. Here lies the beloved...wait, who was she again?"