The UPS shipping guidelines (or at least the practical part of their guidelines) basically state that 2" of packing material must be present on all sides. You're also supposed to use a new box each time, but as long as the box is in good condition, it's usually ok. If you ship a computer, however, you do have to use either a new box or the original box with the original packing material.

Please heed this advice. UPS is infamous for being very rough with their packages; it's one of the ways they are able to move so many packages for so little cost. Basically, if you're not comfortable with the notion of dropping your package to the floor from a height of 4 or 5 feet, then maybe your packaging isn't quite up to snuff. USPS is better with their packages, but I have received Priority Mail packages containing goods which were damaged in transit due because the person packing the item used a box that was far too small for the item to be shipped safely.

Building a supply of proper packing materials doesn't have to be expensive. The packing materials I have are all "re-used". I bring home discarded packing peanuts, "kraft" paper, bubblewrap, and other packing materials home from work, rather than let them be thrown out. The only packing materials I have actually purchased are some computer boxes, packing tape, and address envelopes.

How to properly pack your item(s):

• Find a box large enough to hold your item(s) plus approximately 2" of packing material on all sides.
• Put the item(s) in something, such as an anti-static bag if it's computer components, or newspaper for non-electronics, or maybe a garbage bag if it's an entire computer or something similarly sized. Either way, make sure that your packing materials cannot get inside your item(s). I have had more than once case where I had to disassemble equipment to vacuum out bits of styrofoam that got inside the equipment.
• If you are shipping more than one item, please make sure that the items cannot damage each other. Use newspaper or bubblewrap, for example. Or maybe if the box is large enough, separate the items inside the box and pour in packing peanuts or something like that. Also, put the items side-by-side if possible, rather than on top of each other, to help minimize the risk of one crushing the other.
• Next, fill the box with a bit of packing material (remember: 2" is the golden rule), place the item(s) in the box, and fill up the box with packing material until the box is almost overflowing. Basically, you want the box to be packed "hard". If you have to compress the packing materials in order to seal the box, movement inside the box is less likely, which helps to prevent items from colliding and from settling to the bottom of the box.
• Now it's time to seal the box. Don't use masking tape or duct tape. Period. Neither are designed to seal boxes. Use real packing tape. It's pretty cheap and it does a much better job. Use one, two, or three strips of tape across the top and bottom openings, depending on how strong the tape is and the condition of the box.
• The last step is the label. What I used to do until I purchased address envelopes recently was to laser print an "address label" on a standard sheet of paper, fold it in half, and firmly tape it to the top of the box. I've been told that the problem is sometimes such a "label" can get caught on machinery because there's no adhesive holding it down, and ripped off the package. At this point, your package has no name, and is in limbo... I've never had that problem before, but use this type of label at your own risk. Priority Mail labels are free from the post office, so that's taken care of if you ship by Priority Mail a lot like I do. There are a few options for non-Priority packages, all of which cost a little bit. You can buy adhesive-backed laser labels, or adhesive-backed address envelopes, for example.