I recommend grooming on a counter or table top, not on the floor or in your lap. Just be careful not to let him fall or jump off the counter/table.
Practice putting him on the counter/table at least a couple of times a day. I agree with Teresa, use a lot of massage in the grooming process. Take your time and make it a positive experience. Don't show any anxiety or frustration, but be confident and firm and don't give up. If he knows you will give up, he will keep fighting you and grooming.
If he has a favorite chew, give that to him to distract him from grooming. Praise, praise, praise for good behavior. Make sure you aren't tugging on skin or causing pain. As noted above, start combing/brushing in small sections at the bottom of the hair shaft. Always hold the hair section with one hand to prevent skin pulling. For tangles, carefully pick them apart. I use the sharp end of a rat tail comb. Don't try brushing out a tough tangle or mat.
I highly recommend this brush:
Amazon.com: ISINIS Large Cushioned Hair Brush... Nylon bristles do not sound appealing, but this brush moves through the hair easily. It won't remove mats though. A mustache/leg comb from Madan (mimimomo here sells them) is also an essential.