Sit down with your fiancé before registering and decide what staples you need and extras you would like to have, and take an inventory of what both of you already own. Divide up the list; your fiancé may be the electronics expert, and you might know more about what gadgets are needed for the kitchen. Creating a list will help you feel less overwhelmed when you enter the store and fire up the scan gun.
Don't register for inexpensive items like ketchup or makeup. I knew a girl who registered for mascara and 3 toilet brushes at a big-box retailer, and I remember wondering if she and her fiancé were taking the registry seriously. These are everyday items that you regularly purchase, and while you should have fun shopping, stick to registering for traditional items like bed linens, dinnerware and bath towels.