I have made many decals using Testor's decal paper for inkjet printers.
After I print the decals I let the ink dry for a couple hours just to be sure its dry.
I then coat the decals with several light coats of a clear finish letting the coats dry between applications. For clear finish I have used Testor's dull-cote, Krylon 1301 Clear, and Testor's Decal Bonder #9200. All 3 have worked fine for me but the Testor's Decal Bonder seems like the best one.
After the last clear coat (usually 3 or four light coats) I let the decals dry overnight.
Be very careful when applying, they seem to be a little more fragile than commercially made decals. I always wet the are where the decal is to be applied. Put a small drop of dish soap into a bowl of water and use that to soak your decals and wet the area where it will be applied. Try to get the decal into position the first try and try to move it around as little as possible.
Making your own decals adds to the enjoyment of the hobby.
However, if you decide you don't want to mess with it, don't forget Astronboy and Tango Papa - both great sources of quality custom made decals.
Good luck and have fun!