Try going for a long walk with him first, doing a few ground manners excercise as you go.
When you are ready to clip the only talk should be telling him what you are going to do. This will help YOU to focus. He will respond more to body language than talk. Just an inch or two at first will do.
If your clipper blades are nice and sharp you will NOT hurt him! Don't be afraid of that. If they are dull, you might pull on his hair a little but it isn't going to hurt him.
Does he HAVE to be clipped? If so, then make up your mind you are going to do it. He will get the message.
I have a new shetland mare. She is 4 and was unhandled. I've had her 4 months and I haven't clipped her fetlocks yet. She lets me do her ears, but not her muzzle or feet yet. So, we are just moving along at our own pace; it may be next year before she gets her feet clipped. She is ground driving and doing tricks, but we haven't done the muzzle. Ho hum--it will come eventually.
One thing about working with the skittish horse I have become aware of, and that is holding onto him by the halter. Pulling down on the lead rope puts lots of pressure on the tender cartilage of the nose. I think it is better to have a fence or wall on one side that he can move against, instead of constantly pulling on his nose.
If he is a horse that kicks, I would move him along. I don't think you could ever trust him, and life is too short to keep a horse like that. You did not say if he is a stallion.
Sorry, I don't like twitching. I can see in a life-threatening situation it would be necessary, but not for clipping. Everybody has his own opinion about that, I know.