Consider your new mattress and foundation as "sleep equipment" that needs to be cared for in order to assure the best hygiene and performance. It's important to follow mattress care instructions from the maker of your mattress as products vary greatly. In general however, it's important to know the following:
Proper installation. Make sure your new mattress and foundation are properly installed in your home. Improper installation can damage your new sleep set. If you choose to transport and install on your own, ask the store personnel to give you some tips to help you avoid problems.
Use a protective pad. A good quality, washable mattress pad (and one for the foundation, too, if you like) is a must to keep your set fresh and free from stains.
Let it breathe. If you detect a slight "new product" odor, leave the mattress and foundation uncovered and well ventilated for a few hours. A breath of fresh air should do the trick!
Give it good support. Use a sturdy bed frame. If it's a queen or king size set, make sure your frame has the adequate center support that will prevent bowing or breakage.
Don't remove the tag. Contrary to popular belief, it's not illegal to remove the law tag, but the information on the label will serve as a means of identification should you have a warranty claim.
It's not a trampoline. Don't let the kids jump on your sleep set. Their rough-housing could do damage to the interior construction, as well as to themselves!
No boards, please. Never put a board between the mattress and foundation. It may enhance the sense of support for a while, but it will only make the problem worse over time. When any bed in your home has reached the "board stage", get rid of it.
Out with the old. Now that you've treated yourself to a new sleep set, arrange to have your old bed removed and disposed of. Don't give it to the kids, relatives, guests or neighbors. If it wasn't good enough for you, it isn't good enough for anyone else. Throw it out!