For this step, it's helpful if you have a good eye for centering things. If you don't, perhaps attach the dark template to a very thin piece of copy paper that is the size of your cardfront and measure the center. Open up your card, center the card front overtop of the larger template, emboss.
Next up, center the smaller template within the part you just embossed. Again place the cardfront OVER the template and emboss.
And there you have it, a classy embossed rectangle cardfront. For the card I made yesterday, I stamped first, then did the dry embossing. This made centering the templates even easier. If you want a slightly different look, try flipping the cardfront for the smaller template (i.e. do the dry embossing directly on the outside of the card instead of the inside. You'll get a slightly different look.
Thanks for looking. I hope that helps you! Don't be afraid to try different shapes and measurements!