Determine the weight of the envelope and the postage necessary. If you have a postage scale, weigh the envelope. Visit the U.S. Postal Service website for a chart detailing postage rates for envelopes. If you do not have a postage scale, visit the post office and have your envelope weighed there.
Figure out the number and denominations of postage stamps required.
Place the postage stamps on the upper right corner of the envelope. When more than one stamp is required, begin placing the stamps in the uppermost right corner and place additional stamps in a line across the top of the envelope (right next to each other). Stop placing stamps when you are about 2 inches away from the return address (in the upper left corner). Continue placing additional stamps in another row underneath the first row, if necessary.