Decals, or Transfers, are a good means to spicing up the look of your models. Whether it be a squad marking, runic emblem or even kill scratches. As it is a bit hard for me to scan myself applying decals to a model, you'll have to go without pictures for this page. Sorry. But I'll try an describe the way that I do them as best as I can.
Decals are usually left as one of the last things that are added to my models. So the first and foremost thing I look at before applying a decal is where it is going to go. I find it best to work this out before I have even started painting, as then I will know that the paint should be a smooth an uniform as possible in this location. If you start to get lumps in your paint work they are going to be visible when lying underneath the decal, causing it to push up, and maybe even distort the position of it (mind you, your painting should be smooth anyways). Decals are best placed on large flat areas the aren't going to cause it to crease.
The next thing to do is to have a glass of clean water ready to put the decal in, to remove it from the paper backing. One tip I can give you is to put one or two drops of dish washing liquid into the water and give it a slight stir. This will help the decals slide off of the paper, especially from those decal sheets you've had lying around your house for a long time. Just don't put in too much, otherwise you'll be up to your ears in bubbles.
The next thing to do is cut out the decal, using a sharp hobby knife. If it is blunt, you risk tearing the sheet and possibly the decals. Make sure your cutting surface is protected adequately enough so as not to score it. A wad of news paper does it for me. I usually cut around the decal in a square or rectangle shape, keeping well clear of all the decals. Please do this carefully, so as not to slip and cut yourself. Just apply moderate pressure, and guide the knife carefully. You should come off injury free.
Once it is cut out, I then use a pair of tweezers to hold onto the edge of the paper (not the actual decal) and immerse it in the water. After a one minute wait, the decal is usually ready to be applied to the miniature. Place the decal, still with the paper backing, onto a flat surface and use an old brush (which has also got water on it) to check and see if the decal is completely sliding around on the paper backing. If it isn't, just put it back in to the water with the tweezers for a few more seconds.
Never try to force a decal off of the paper. You risk damaging it. Just make sure that the decals slides freely on the paper backing. Then I put a wet brush onto the surface where the decal is going to go, just to make sure that it is wet also. This helps sliding it from the paper backing to the figure. Just make sure that you have got the miniature in a good position to be able to put the decal on in the appropriate place. Then with the tweezers holding the decal in one hand and my brush in the other I continue forth.
I rest a corner of the backing paper onto the area where the decal is going to go (this should be a wet surface as previously mentioned). Then with the brush tip I push the the decal along the paper, off onto the wet surface of the figure. Now you can put down the tweezers and pick up the figure. The reason I wet the surface is because it also helps in sliding the decal around until it is in the desired position. So I use the brush to do this. A poke here, a prod there and I get the decal where I want it. Then I use a piece of absorbent tissue paper and careful use the corner of it (for accuracy) to soak away any excess water. Once all the water is pulled away, I then use the flat surface of the tissue paper and carefully apply it the surface of the decal and give a slight push or squeeze. This will pull out any water that is still sitting under the decal. Viola. One decal complete.
As most decals seem to have a glossy surface, this can be eliminated by your final coat of matte varnish.
