Once you have started moving in and out for a while, take the dildo out and relube.
You may want to switch positions now so that you can try something new. Try to pick a position like the one shown where you have easy access to his dick.
Now its time to really fuck him. It should go in much easier this time, but remember to be really slow.
Once its in and you can move in and out freely. Start slow and start picking up speed, this will drive his prostate so crazy that when you really start going to down there will be precum. While your fucking him start jerking off his cock, and continue this for as long as you both are enjoying it (try to keep it up for at least 5 minutes, but thrusting like a man for a long time isnt as easy as they make it look)
When you've gone to town in your mans Anus and fucked him like you were the man and he was your bitch press continue