You have already gotten some great advice -- I just want to throw my vote in to NOT sedate a puppy for grooming! That is only done as a very last resort for a dog that is having severe anxiety himself -- in other words it is only considered for the health of a dog and NEVER for the convenience of the groomer!
My Ben did not like grooming either. I keep his brush on the table beside the chaise we share in the evenings. He likes to curl up with me at the end of the day. So, he gets a little brushing here and there. He doesn't mat much any more but when he was a puppy, that fine downy hair on his inner legs would mat. I would rub a little Cowboy Magic in them and then gently pull apart the mat with my fingers then brush through. If he gets a tangle now, I do as suggested already, hold the hair firmly between the tangle and the skin, then work the tangle out without pulling the skin.
Another big help was getting a proper brush. I ordered a Madan pin brush from Mimimomo (
http://www.yorkietalk.com/forums/yor...shes-sale.html) and WOW what a difference! It is so gentle to use on our Yorkies! Ben does not seem to mind being brushed at all now. I think he has finally found out how good it can feel. Believe me -- it really does make that much difference.