Take their penis or strap-on in your hand and help guide it into you. A little lube can help them slide in easier, especially if you’re feeling nervous. Lower all the way onto them. Then, slowly start rocking your hips back and forth in the direction of their head. Keep your pelvis in contact with theirs at first (remember, no bouncing unless you want to!). Then try grinding your hips in slow circles. Experiment with clockwise and counterclockwise movements.