The trick is to follow the mirror, signal, maneuver method. In other words, you don't signal until you know you have a gap to change lanes into. If you signal

The trick is to follow the mirror, signal, maneuver method. In other words, you don't signal until you know you have a gap to change lanes into. If you signal first without checking for a gap first, then you're treating the signal as a way to ask for permission to change lanes. Other drivers may or may not allow you to do so.