After level 30 the difficulty of Neverwinter jumps up. However, unless you are rushing to end game, I don't think power leveling is really going to benefit you.
Mitigation in Neverwinter means exactly what the actual definition of the word means.
So for example, Ray of Enfeeblement has the following description:
Ray of Enfeeblement: Over several seconds, deal damage to your enemy while decreasing their damage and Mitigation. Debuff duration
increased based on stack of Arcane Mastery
SO, what this all means is for a period of time you've lowered the targets ability to reduce the damage from your incoming attacks.
Well how is the target mitigating (there's that word again) damage from your attacks in the first place? Good question, glad you asked.
Damage Resistance IS mitigation.
Damage Resistance decreases the amount of damage you take from incoming attacks. Defense helps to increase this stat.
Therefore, if you put this all together using what you just learned (stay with me now) it goes something like this...
"Target X" has a damage resistance stat 21.2%.
You cast Ray of Enfeeblement on Target X which reduces his damage mitigation by 15%.
Over the next several seconds, Target X's Damage Resistance (ie: mitigation) is effectively 6.2%
21.2% - 15% = 6.2%
Best Answer
I Find the best way to do this is guild quests. They can produce a massive amount of XP in a short space of time. I only recently started playing and have 3 Characters at level 70 now, I mainly jump from level 40 to level 50 odd just on following the guild quests. Skirmishes, Dungeons and PvP can also provide you with a fun way to gain XP as well as some decent AD.