First of all you will need any type of heavy or light armor, you will also need to lower down the difficulty all the way.
Make sure you are wearing the armor while doing this (it is 100% more eficient if you wear a full suit of the same armor).
Next make sure you have a lot of healing potions.
Now here is what you're gotta do, go to any city, most preferably Cheydinhal, then go the castle guard barracks.
Once inside punch one of the guards only once! After he tells you to pay the fines or go to jail don't choose either one, chose the one that says resist arrest and after you do that you will see a swarm of guards running towards you to attack you.
Just stand there and let them attack you (most preferably in a corner).
Whatever you do, do not attack the guards!
After being attacked for a couple of seconds your light or heavy armor skill will go up really quick.
If you start to get low on health just drink one of the potions. Keep this up until you reach whatever level you want.
Also make sure you have at least 60 coins because if you hit the guard one time that is how much it is for the bounty.