They are weak to fire (as someone said that already).
If you are fighting them in wilderness, try to climb up on a rock/mountain, where they can't get you and use your firebolt/whatever distance spell/bow on them.
Use Conjuration summons. Monsters to keep them busy, Swords and Axes for massive damage.
Use Shouts, they are not just useful against Dragons, they are useful against monsters too!
Also remember, that they regrenates health all the time, so try to kill them fast!
Each time you level up, they are easier to beat.
Hope any of those tips helps you.
