How do i ollie right!!?

ok heres the thing i know how to ollie,but my back wont pop up,its weird,this is wat i do i put my bottom foot on the end of the tail on the ball of my foot and my front foot in the middle i hit the tail down real hard while doing that,my front foot slides forward while jumping.oh yeah i also lift my back foot into the air to once i pop it.It feels like im doing it right but the back only pops up 1 tiny centimeter. my board is also old like no grip tape and its just crappy,but im getting a new one in two months but i just want to be able to ollie. anything would be helpful.