One of the tricks I have come to rely on when making my own decals is to use a piece of foam board, like the type found in Michael's Crafts or at WalMart in the office supplies aisles. This provides me with a nice flat surface to tape the printed decal paper on before overspraying with gloss clear coat.
I cut a 2' x 3' board into several different sized pieces- as when I print on the 8-1/2" x 11" decal paper, I then cut off the printed portion to preserve the remainder for re-use. Since most of my printing is done in portrait (vertical) format, my cut-offs tend to vary between 8-1/2" wide by 1"to 5" long. I let the printed (ink-jet) sheet air dry for 24 hrs, then cut off the unused portion and store it back in a plastic zip-lock type bag, away from light (either sunlight or artificial).
I then tape the printed piece of decal paper to the foam board with blue painter's tape, and spray my gloss clear coat on- waiting another full 24 hrs to begin cutting and applying the decals on my project.
The foam board (in the cut down smaller pieces) provides a consistent flat surface for the clear-coated paper to rest on, which ensures an even thickness as the spray dries. Always set the sprayed paper-and-foam-board on a flat shelf, away from house traffic, so additional dust specks do not fall onto the drying surface. If you have a lot of carpeted rooms, make an effort to find a solid floored room space (hint- if teenagers are present, NOT the bathroom!) where less dust can be released from walking around.
One other idea- when I spray the clear coating, I usually do so in my large paint booth with the extraction fan running to remove the fumes from the spray. Do not let a fan (creating air movement) continue to play over the sprayed surface after you have completed spraying, as further air movement may (and it HAS happened to me!) create eddies in the clear coat as it settles onto the decal paper, resulting in noticeable ridges when the clear coat has dried.
Hope this helps...
Cedarwoodron