Part of the decision process is easy - use White Decal Paper. Buy the paper for your specific type of printer - Inkjet or Laser. Put the paper in the printer, open the file, and print.
If using an inkjet printer, after the sheet has printed, allow it some time to dry (15-30 minutes), then spray a light coat of clear gloss paint over the sheet. allow this to dry fully, then spray a second coat. This will seal the sheet so the ink doesn't run. (This step isn't necessary when using a laser printer.)
Application is the same as for any other decals (I recommend Winterdyne's tutorial in my sig). Note, however, that as your using white paper, when you cut out the decals, you will have a white edge to them. To fix this, cut the decal a bit wide before applying. Once the decal has fully set, use some of your background paint (black in this case), and use that to cover/blend the decal edges into the model background. That was the technique used on the Imperial Raptor on the missile pod on my Deredeo below.