Replying to 270 out help/ CANT SCISSOR!

ok so ive been trying to get 270s out and im having problems! Ive tried front side, and back side, and i just cant do it! Im getting really frusterated. Anyways, So I cant scissor? Ive been trying them on flat boxes and a narrower up box? we dont have any good rails to try them on. I need help! Do i need to pop more? or is all in the scissor? Are there any good vid tutorials or what foot to scissor when riding on a certain side? Gah, i need help...

Thanks
(+K for good answers)