Training on slimes is slightly slower than using a monk because when a slime dies it takes a few seconds for the new one to get to you.

* Get 1 wild slime and find a place where you can block yourself in with only 2 monsters attacking you.
* Hit the original slime so you can tell it's not a summon, don't kill it.
* Now just hit the summoned slimes for your training, the wild slime will summon you an infinite amount.

You will probably need to use a very weak weapon and if your skills are high even using weak weapons you will kill the slimes fast.