Some friends and relatives may want to get you a gift as soon as they hear about your engagement, so it's best to register, at least for a few items, early on. If you're having an engagement party or a shower, try to register at least a month beforehand. Don't feel pressured to make all of your choices at once; you can always go back and fill in or edit your list later.
While it's possible these days to set up a registry and pick out items entirely online, you should visit a store at some point to take a look at everything in person. In addition to everyday items, consider special pieces. Select items in a range of prices, based on your current tastes. Keep an eye on your list; if items are sold out or discontinued, replace them with something else.