Personal Advice

[Maverick]

"You might also want to try with him sitting down on you. This puts him in full command here and gives him the feeling of control thus he may actually relax a lot more into."

What Bowyn says here in my experience was the most important. Let the "bottom" be on top, then he can be in total control, thus as relaxed as he can be (which is tough cause it's all new) and slowly work you in. It may take a while, and there may be several starts/stops and re-lubes, but just have him take his time. Practice does help and it gets easier over time, so don't get discouraged...