First write a letter to the defendant (your "judgment debtor") 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 doesn't get the money into your hands, you'll need to identify a likely collection source. If your judgment debtor is working, wages are usually your best and safest bet. You'll 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. You'll have to pay a small fee, which will be returned to you, assuming the collection effort is successful.