Dave - they're both pretty easy to use if you're careful...
First make sure the area under where the decal will sit is nice and glossy, for cars this won't be a problem. If you are doing something with a dull coat just gloss the whole model so it looks even when you dull coat it in the end.
Wet the decal, while it is soaking/loosening from the paper put some Microset down with a brush where the decal will be. Slide the decal off and position it, drop a little more Microset on top of it. When it is settling down after about 5 min or so take a dampo paper towel tip and gently pat it down pressing it into the detail. You can use more coats of Microset at this point if it isn't behaving properly.
If it doesn't sit down like you like it, it's time to bring out the big guns... After the decal is dry, brush some microsol on top. Don't be scared but most probably that decal is going to wrinkle up like a raisin (or worse)
Biggest tip: DON'T touch the decal after using microsol until it is completely dry!!! (I would give it several hours) Voice of experience here, it's a fast way to destroy a decal!!
It should be lying down flat once it dries... if not then hit it again with the Microsol. When it is dry and cured (at least 24 hours) I would Future over the decals. The only reason I say this, is even if you plan on using a enamel or lacquer top coat, the future will help protect the decal from the strong solvents. It also makes it harder to scratch or tear them until you do gloss coat. If you don't like Future or don't use it, go ahead and gloss coat them at this point. Good luck to you!
And again, the biggest tip I can give you is handle the decal as little as possible when using Microset, and if you need to move the decal use Microset to re-wet it again instead of water.
Number two would be don't touch that thing once the MicroSol goes on... I can almost gaurantee bad things will happen!!
Good luck to ya!! I think you will love both of them (Microsol/Set) once you get a few decals down with them, they'll look almost painted on!!