There should be good information on Monkeybar’s thread. He recommends using tape over your glans; however I never got the tape to stay on. He recently came out with a compression sleeve to be used in place of the tape.
My autoextender came with a hard plastic cap. If this is what you have, locate the small vent hole and mark it with a black permanent marker so you can see it through the silicone sleeve.
Stretch the silicon sleeve over the open end of the cap. Now slowly work the sleeve up toward the top of the cap with your fingers until at least 2/3 of the cap is covered by the sleeve. Now roll up the other end of the sleeve until it is rolled up around the bottom portion of the cap. Press your glans hard against the inside top of the cap so that your meatus is tightly squeezed against the cap. Roll the sleeve over the end of the cap and down your shaft.
Locate the vent hole and push your dick up against the cap while rolling the top of the sleeve down over the vent hole. You may hear a small amount of air released through the vent hole. Roll the top of the sleeve back over the vent hole. You should now be ready to attach the hook to the cross bar and be on your way to a longer dick.
I ususlly insurt my shaft through the base of the extender before applying the plastic cap.