If you are kneeling, you can rock back and forth (to and fro), side-to-side, and/or you can undulate by going in a circular movement that is sometimes very effective as it will stimulate the deep-seated nerves of the penis in the abdomen in addition.

Up and forward then down and back while sitting upright using your knees as a fulcrum, then lean forward and go back and forth by rotating hips, alternate between the two positions changing speed as it suits you.

I used to have the same problem! My best answer is to ask him to put his hands on your hips and guide you to what feels good to him. Along the way, you'll get to find out what feels good for you, too, and then you can go back to it later.

that was great advice for me too (above) as i have the same problem,wont he think im no good though?as last time i obviously wasnt doing it right and it was really awkward so i stopped and never had the gutts to try it again even though he keeps hinting!!:(

if you think your not doing a good job just as him to guide you

In anything we do it, takes practice to become good at it. Don't worry about doing it wrong and just enjoy. You'll get there.