Get some Testors decal applicant/solution, really helps them go on better, there are directions on the label of the bottle. Also, suggest you use a VERY small pair of scissors. I use a soft-bristle brush to coax the decal off the backing sheet and onto the model...this is where the Testors stuff comes in handy, I think it makes the decal easier to move around.
And, of course, you'll need a good deal of patience, and I would suggest you have multiples of the same decal.