When you're moving, you'll need to fill out of change of address forms, of course (if you care about getting your mail), which you can print out from www.
usps.gov. But you should also consider how your mail gets forwarded to you.
Ideally, you would fill out your change of address form up to 30 days before your moving date. You can expect your forwarded mail to arrive 3-5 days after that date. The post office will send a confirmation letter to your old address and one to your new address on your moving date.
First-class, Priority and Express Mail are forwarded for 12 months, with the exception of those marked "Do Not Forward." Second-class (periodicals) is forwarded for 60 days at no charge. Standard Third-Class (circulars, catalogs, advertising) is not forwarded unless requested. Fourth-Class (Parcel Post) is forwarded locally for 12 months at no charge. Mail forwarding is free, except for parcel post deliveries forwarded outside the local area.
Notify people, companies that bill you, etc., 30 days before your moving date. Notify magazine/newspaper publishers and other business mailers 4-6 weeks before.
Mail marked "Do Not Forward" is returned to sender (but not "address unknown") - with the new address - if your move is permanent.
a shout out to the g's at MoversNet