My most recent character is a dual wielding mage warrior. I use bound swords and at level 26 my conjuration is 90. I bought the 'conjure dremora lord' tome from Phinis and was wondering if there is anyway of increasing the damage the dremora do. I know the perk Atromancy doubles the duration but does the perk Elemental Potency affect the lord too? The dremora lord uses fire but he isn't very strong. I have one more perk before I get Twin Souls so I might just use two fire or storm potent atronachs because they seem stronger than the dremora lord.

Nope, Elemental Potency doesn't affect the Dremora Lord. Your character's level however, does.

Have a look at http://www.uesp.net/wiki/Skyrim:Dremora#Melee_Fighters.

Two of them are great. They are very neat and don't cause problems with movement, which is a major issue with the frost and storm atronaches. I tend to use undead up until about level 30 and then switch to dremora lords. I also have illia and Barbas so damage is not a problem.