There are 7 designs pre-created to choose from that I have found popular at shows.  

One of them can be customized with the person's name and number with a "if found please return to".  These are great for keychains or for luggage tags and I usually put this on one side of the keychain with a design on the back side.  They were also very popular at my last show.
 

Set your keychain into the machine.  

I suggest either using a jig or adding a bit of tape to make sure the tag stays in place.

Refresh the camera view on your ultra and line up the design with your tag (or use framing lights if on the F1 original).

I like the way that 40 power 250 speed and 2 passes came out.

Not all tags are created equal.  I included a picture of the same design with the same settings on the same brand of keychain that is a different color and you can see it comes out a lot more subtle on their white tags.  All of the other colors produce the pretty dark black.  I still like the lighter one but be aware that there may be variations.

I engrave the front and the back of my keychains but they don't have to be the same designs so feel free to mix it up, use complimenting designs, or add custom name or contact info on the back side.