1. Check your hazards. Turn on your hazard lights to see if all 4 corners are blinking. You can tell if your bulbs are bad quickly.
2. Check your bulbs. Look at bulb for blown filaments, and black soot.
3. Check your connections. Wiggle the wires with the signal on.
4. Check other direction. Sometimes the turn signals are wired into the same relay. So basically both signals would have the same problem, if it was the relay.
I had a Mercedes C300 with halogens and that sombytch was sensitive with grounds. Just wiggle those wires around, and tighten connections if you see them loose.