Some good advice above. I've decaled many teams and learned a little along the way. Here's a list that's by no means exhaustive.
1. Clean up the figure with a nail file before you start. Use it to remove any burrs or ridges particularly along the shoulders. It'll make applying the decals easier.
2. Paint the figure (except for the base) but don't worry about being perfect because you'll go back and clean up the lines after the decals are applied.
3. Apply the decals - Sleeve stripes are the hardest, followed by sock stripes because the surface isn't completely flat. Numbers, names, and helmet logos are easy. Precut decals will make the job easier and faster.
4. I put the decal in water. Some use a wet sponge. I use an x-acto knife to pick it up and a toothpick to maneuver the decal onto the figure. Don't force it off of the backing. If it doesn't come off easily then put it back in the water. Keep a cloth handy to dab up any excess water once you get the decal positioned on the figure.
5. Once the decals are dry they're very fragile so try not to touch them. At this point you may want to apply a little solvaset to get them to lie flat. Just a touch will do it.
6. Once that's done I go back and clean up the paint lines particularly along the sleeve and sock stripes. This is usually when apply the skin tones.
7. Once everything is done, paint the base. The reason for doing this last is because that's where you handle the figure and the oil from your fingers will screw up the paint.
8. The very last thing I do is apply a sealer. I use Martha Stewart High Gloss Finish and coat the whole figure. This will protect the decals and, in my opinion, make them look great. Once it's dry you can handle the figure and not screw up your decals.
I hope that helps. Patience is the key. Take the time to paint clean lines and apply the decals and you'll be happy with the result. I've applied thousands of decals and still screw them up sometimes.