First write a letter demanding payment. Mind both your Ps and Qs; keep your missive polite and straightforward. If you need help with this - especially the all-important Ps and Qs part - you can find a sample in Everybody's Guide to Small Claims Court, published by Nolo.
If this genteel approach does not get the money into your hands, you will need to identify a likely collection source. For individuals who are working, wages are usually the safest bet. You will need to take an official copy of the court's judgment to the sheriff or marshal along with information about where the judgment debtor works. A small fee will be required which will be returned to you, assuming the collection effort is successful.