Print a test label sheet and cut out one label to make sure that it fits your keys perfectly.

When you're satisfied that the labels have printed correctly, print a new sheet and cover each row of labels with tape.

The tape will provide a durable surface to press and protect the label.

The best tape for this is the invisible kind which is often marketed as being able to be written on, non reflective and invisible. Normal tape (the cheap shiny stuff) is no good because over time it will yellow and peel. Invisible tape doesn't suffer from this problem.

Using your fingernail, rub firmly over the tape to make it stick properly. You'll see the blacks get darker as you do this.

Use a ruler and blade to carefully cut out the labels. Scissors can be used but it's harder to do.

Note:

I used a laser printer for my labels; I'm not sure how ink will react to glue. I'm sure it will be fine but if the results are unsatisfactory, take your image file to your local print shop and get them to print it for you. You may also choose to have them laminate the page for you instead of you using sticky tape. Get 2 sheets printed; one to laminate and one not, and experiment.