I need help on these two "techniques"

Lie down on your side and hold onto your penis with the "Backhand" grip. Roll over further and brace your hand against the bed, and thrust your penis in and out of your hand. This closely mimics the movements of intercourse. It's a very different feeling to masturbate by moving your pelvis rather than your hand. It's also fun to put your other hand down and feel your scrotum moving back and forth as you pump in and out of the "vagina."

this seems like the hardest one to do...

i cant seem to move my penis in and out... I can hardly move it at all

I saw this..

THE BAGGIE & THE MATTRESS

Get a plastic sandwich baggie and put some Vaseline in it. Then put your penis in and squish all the Vaseline around so it covers your penis. Once that is done, kneel in front of a bed. Lift the up mattress and put your penis, with the baggie still on it, between the mattress and the box-spring. Start pumping as if you were having sex. When you're done, all you have to do is throw away the baggie.

And I was wondering if it would work with a bag this size:

http://www.minimus.biz/images/J02-0227901-9400bg.jpg

 

Anyone? I can do the baggie, but I dont get any pleasure from it

 

Firstly, what's the size of your dick. Secondly, what's the exact size of the bag, a thumbnail doesn't cut it.