When you dispose of sensitive documents in garbage or recycling they can be snooped by your neighbors, waste management employees, and strangers walking down the street. You may not want to take advantage of that low-low interest rate pre-approved credit card offer you got in the mail, but somebody else might really like to use it at your expense.
Shred any unnecessary documents that contain your Social Security number, medical insurance numbers, birth date, credit card numbers, or financial institution account numbers.
A paper shredder is much better than tearing documents by hand.
Don't have a paper shredder, or have one that's too weak to handle the mail you get? Many communities offer "shredding day" events when you can bring your old-but-sensitive papers to a credit union, bank or community center and have them shredded and recycled for free by an industrial-strength machine. Here's a calendar of upcoming shred days in Washington state.