It's a good idea to have a plan for what you want your hair to look like. If you go to almost any of the chain haircut places they usually have books with different haircuts for guys. Or you could always check out an online site like
this one or
this one. Once you have a sample, you could always print it out and show them. Then any stylist should be able to cut it right.
Or just ask the stylist, tell them you want a short cut and ask if they have any suggestions. I am sure they would be able to come up with something. Sometimes the hardest thing to do is actually the simplest.