Hi Davy,
With Microsol, you have to be careful, but it is easy to use. The principle is the same with when I decal cars. While the decal is sitting in water, take some Microset, brush the area where your decal is going to go. Apply the decal, get it into the right position, then apply some Microsol to the entire decal with a brush, then don't do anything!! Just let it sit. It will start to wrinke, but don't do anything with it, it's supposed to do that. Come back after 10 or 20 minutes, you will find that the decal has conformed to the surface, zimmeret, etc, and is nice and flat. Wait overnight, then either airbrush or hand brush on some clearcoat to seal in.
If your decals look like they are cracked from age on the decal sheet it self, try Microscale's Decal Glue? (I think that's what it's called) Brush on a coat while the decal is still on the sheet, and when dry cut out and trim the excess as close to the decal and apply like you normally would. Hope this helps!
-Kelly