I'm not expert in applying these, but relied on my memory in applying decals to models when I was a kid. I soaked one of the 1st edition decals in a bowl of water for 1 minute and it slide off beautifully. It might take 5-10 seconds longer with the 2nd, 3rd (larger) versions. Test it with your finger tip and you'll feel when it begins to release from the paper backing. You have a several seconds to make sure it's positioned correctly before it starts to take a set but once it sets you will not be able to move it. I lightly blotted the surface with a paper towel when I had it where I wanted it, starting in the middle and working to the edges. A sponge or a soft lip spreader as used in body work might be work as well. I understand that some may use a drop of liquid soap in the water to make it even easier to slide but I had no issues with plain water. I also have read that many apply a clear coat (acrylic I assume, but I have not tested this myself) to make it more durable. These are professionally printed and do not require trimming - ready to apply as they are.
I know there are other Cabers with more experience in applying these - any input appreciated -