SKATEBOARDING: HELP ME WITH MY OLLIE PLEASE?

okay so my ollies are good. its like pro ollies. i could do em off stairs, gaps, etc. but problem is my ollies arent mastered. often, it would do a ghost ollie. my ollie wouldnt stick to my back foot, it would look like a crap ollie. and THE BIG PROBLEM. is. sometimes. my foot slides up, but it slides up like a ollie north, comes off thenose, and i end up landing it with just my back foot. its rlly annoyying. how can i fix this? please answer asap :]