I think one of the best things you could do would be to build your Smithing up. Once you have a high level of blacksmith ability, you can forge your own weapons. They'll be a lot stronger than weapons you find lying around, and it will make the dragon battles a lot easier.
Well, this isn't really an attribute or a skill, per se, but it's a lot easier to kill dragons if you know certain spells. If you know the Ice Spike or the Lightning Bolt spells, for example, you can use one of them to stun the dragon in mid-air and coax it into landing. Once you get it on the ground, you can use a high level shout (Unrelenting Force, for example) to open it up to melee attacks.
I personally have really high archery skill - I can happily take down a dragon in between 6-10 arrows, depending on the level of dragon. This is a good way to go as you can hit them from a distance, and also get a few shots in whilst they're airborne - no waiting for them to land!