As already said the glue needs to be applied very thinly & then given plenty of time to dry. Once the glue is completely clear I apply the foil & rub with a cotton bud. As you are rubbing you can usually see the foil starting to seperate from the backing film, dont try to pull the backing off to early, if you have rubbed sufficiently it should lift away nicely.
The biggest problem I have had with the finished effect is with the metalic effect foils which, once I applied the sealer, started to look as if the foil was cracked. I did once see a picture of a metalic foiled nail which was descibed as a "pretty antique look" but to me it just looked cracked :lol: So I'm not sure if it was just my application or if metalic foils all do that.