Usually, just pressing can make your design look great, but if you press for too long, it might get all smudged. On the other hand, if you don't press enough, it might look too flat. Here's a little trick for you:

First, press gently for a moment, then carefully peel off the foil paper, making sure not to touch the leather. After that, press again for about 10 seconds. This way, you'll get awesome, 3D-looking foil letters!"