I've been using clear decal sheet for some time and have just ordered a fresh pack together with a pack of white decal sheet, (which I have never used before). These decals tend to be really thin and difficult to transfer from the backing sheet to the model. What you need to do is spray on a couple of coats of clear gloss lacquer. This gives them a bit of body ...enough for them not to curl up or break apart when you apply them. For small decals ....eg: doors on my 1:600 liners / ships' names etc I simply brush the lacquer on rather than messing about with my airbrush. When they dry you just apply whatever final lacquer coat you want to finish the whole of the model in .....Gloss / Satin or Matt.