Really easy and fairly safe way is to buy a house stand in front of it and shout at the gaurds. They will fight back and try to kill you. Just stand there and take the abuse and when your health gets low walk into your house to let it refill. Then walk back out to the waiting mob of guards and repeat the process. It will take a while and you may develop a bit of a fine but if you can afford it its worth it. Especially compared to how much the trainers cost.

A really easy and fairly safe way is to buy a house, stand in front of it, and shout at the guards. 

They will fight back and try to kill you. Just stand there and take the abuse, and when your health gets low walk into your house to let it refill. Walk back out to the waiting mob of guards and repeat the process. 

It will take a while and you may develop a bit of a fine, but if you can afford it it's worth it, especially compared to how much the trainers cost.