When putting mail in an envelope, the printed side should face the person who will be getting it. The easiest way to do this is to put the printed material on the flap of an envelope. Put folded mail into the envelope so that the last fold is on the front.
When you put something in a window envelope, the address of the person who will get it should face out through the window. Before you send the mail, make sure the whole address is visible, including the zip code. When you put things in an envelope, you should also think about the right size. Personal letters and bill coupons can go in small business envelopes, while long letters and business mail can go in number 10 envelopes.
When folding a letter, you should start at the top and work your way down. To make the first crease, the fold should be a little less than one-third of the way down the page. Before putting it in the envelope, the last crease should be folded over the top half to make a rectangle. Fold mail three-quarters from the bottom to the top to fit it into a small envelope. Fold the paper again from right to left by one-third of its width. Fold the left side in to finish the fold, and then put it in the envelope.