Look twice
Before you turn left across oncoming traffic or change lanes, look twice. The first scan picks up cars; the second scan often finds the motorcycle that the first scan missed. Motorcycles are narrow and can hide behind a car's A-pillar at exactly the wrong moment.
Increase following distance
A motorcycle can stop in a much shorter distance than a car. The three-second rule is not enough; use four seconds when following a motorcycle so you do not run them over if they brake hard.
Lane position respect
Motorcycles are entitled to a full lane. Do not try to share. Lane splitting — riding between lanes of stopped or slow traffic — is legal in some states and illegal in others; either way, do not change lanes when you see a motorcyclist filtering through traffic.