I'm gonna sort of abbreviate those instructions for my purposes here though. First off, to apply decals you'll need a few things:
Microsale Industries Micro Set and Micro Sol Solutions (view here)
A pair of tweezers
A sharp X-Acto type knife and cutting board
a small sponge (the ones that GW sometimes puts into blisters work PERFECT) and something to put the sponge and some water in (maybe a small plate?)
Gloss Varnish (from GW or wherever)
OK first, cut the decal out of the decal sheet. If you angle the sheet right you can see where the edges of each decal is and you'll know how you need to cut it out. Cutting just outside of that decal's edge is probably best so you dont damage the decal itself.
Next, put water into a small plate or something else to hold the sponge and make a wet palette.
Now, paint Glossy Varnish onto the area you want to apply the decal. Apparently you get less bubbles/folds etc if the surface is smooth and not porous. Let the varnish dry.
Next put your little decal onto the wet sponge. You'll see it soak it up pretty much instantly.
While that soaks a little bit, brush some Micro Set (make sure it is SET and not SOL, blue bottle!).
Once you cover the area you want to apply it too with Micro Set solution, use your tweezers to get your decal from the sponge. You can use one of the tweezers to edge the actual decal off the paper backing by now. You should be able to just grab the decal with your tweezers and slide it off once its part way off.
Place your decal and set it how you want it to be, because of the Micro Set solution you'll still be able to move it around and adjust it until its perfect.
Once your happy with the placement, use a dry brush to dab the decal and surrounding area to remove excess Micro Set solution.
Once its set and a dry, dab small amounts of the Micro Sol solution (RED BOTTLE). Don't go too crazy with this stuff, just a little bit will do. Put it on the actual decal and around the edges. Again, use a dry brush to remove excess Micro Sol solution. Let this dry. You may see some "wrinkling" this is normal after the fluid dries, it will flatten a bit if you got the excess fluid removed.
After this is dry, but another coat of Glossy Varnish to protect your decal. This step also helps remove the decal edges and smoothes things out.
If you like you can Varnish with a Matte Varnish after this step.
I tried this process first on a Tau Crisis Suit I am finishing up for a tournament in May. I put a bonding knife icon on its chest and then a normal Tau symbol on his Jet pack.
After I was confident with the process, I put on the 4th Company symbol of the Knights of Baal on the tail of the Stormraven. These are the only decals I plan on using since used so much iconography bits on the rest of the ship.