Mail forwarding ensures that you continue to receive your mail and gives you time to notify everyone of your new address. This includes everyone you do business with or care to keep in touch with.
To be thorough, it's best to make a list. You'll want to include the following people:
To make sure you don't overlook anyone, check your list against the mail you receive every day. Save envelopes and mailing labels so you'll have the addresses handy when you send out change-of-address notifications.
After you move, you might still find that you missed a few associates. Keep the yellow address change stickers the post office uses when forwarding mail to identify those people you still need to notify.