Fancy chemicals make them work better, but if your mini has flat panels to put them on, straight water should be fine. My procedure for decals is as follows:
Coat the mini with a layer of clear gloss spray paint, or at least brush on a patch of clear gloss paint where you plan to place your decals. You really want the gloss, because it provides a smooth surface for the decal to stick to. A matte or bare paint surface is rougher, so you can end up with tiny bubbles trapped under the decal, giving the transparent bits a silvery look when they should be invisible.
Cut the decal out of the sheet (as close as you can to the edges of the image without actually damaging it) and dip it in a shallow dish of water.
Wait 10-30 seconds, or long enough that you can push the decal off the backing paper using a paint brush and almost no pressure. Using said brush, slide the decal off the paper and lift it out of the water on the bristles of your brush.
Place the decal on the mini, roughly where you want it to end up. Dab away most of the water using a bit of paper towel, then use a second brush (the kind that's gotten too stiff from use to be much good for actual painting) to push it into the exact location you want.
If your decal was placed on a smooth panel, then at this point you can let it dry. If it is sitting on any lines, crevices, or other details, dab a drop of decal solvent onto it. This will soften the decal so that it will 'flow' into the crevices when it dries, though for large gaps you may need to push it in with your brush. Be very careful, as softening the decal makes it very easy to tear it.
Once all of this is done, you can let everything dry, seal the mini with matte clear spray, and call the mini finished. :thumbsup:
