Understand how to open a basic pin-tumbler lock you are locked out of — for your own property only.
Only do this on a lock you own or are authorized to open. Picking someone else's lock is illegal; if in doubt, call a licensed locksmith.
A pin-tumbler lock has spring-loaded pins that block the cylinder from turning. The key pushes each pin to a "shear line" so the cylinder can rotate. A pick mimics the key.
Insert a tension wrench into the bottom of the keyway and apply gentle, steady rotational pressure in the direction the key would turn. Too much pressure jams the pins.
Insert a pick above the tension wrench and gently push each pin up until you feel it "set" with a slight click. Work the pins until the cylinder rotates and the lock opens.
If it does not give after a few minutes, stop forcing it to avoid damaging the lock, and call a locksmith. Many lockouts are solved faster by a spare key or a pro.