I've had good luck with my decaling so far. With Testors decals. what I do is this: I put the decal in the water for about 10 seconds, then set it on a paper towel for about 60 seconds more. (other brands may suggest different times then I offer here.) Then I take a straight pin, or the point of an exacto blade, and gently slide the decal just a tad, just enough so it leaves a tiny bit of paper without the decal film covering it. Grab that tiny piece of paper with tweezers and lift the decal/paper up.
Now, put some water on the spot where the decal goes, or you could use some microscale micro-set. I've found the water works just fine. Still using the tweezers, set the edge of the decal about where it goes, then use the pin or blade point to hold the decal down to the surface while pulling the paper out from under it with the tweezers. Now the decal can be moved around a little to position it. A paper towel point can be used to soak up extra water around the edges, just don't touch the decal.
Let it dry a bit. Then If you see any air bubbles under the decal, poke them with the pinpoint. Also, if the decal is going over rivets or uneven surfaces like door edges or whatever, you can poke that area with the pin also. Use microscale micro-sol to coat the decal and the edges. The itty bitty holes will allow the micro-sol to get under the decal in those spots and will make it snuggle down and conform to the surface irregularities. Let that dry.
If one coat of micro-sol doesn't get it all snuggled down, or if there are still air bubbles, use the pin to poke more holes and put another coat of micro-sol on. Now, one warning, once the micro-sol goes on, do not try to move the decal, do not disturb it, because it will be very soft and will get messed up.
Once it is all down and dried for a day, use some dullcoat over it, this will help hide the edges.
Hope this helps. Although I am still fairly new, and haven't done a ton of decals, this technique has worked great for me.