I'll share what I've done to overcome my turbulence anxiety in the past as it was really getting to the point of interfering with my flying.
It comes down to visualising flying and visualising your feelings. I remember my early experiences of flying, about twenty years ago. I was very excited about it and often used to sit in the rear of the aircraft for the view, not knowing or caring that this is the worst spot for turbulence. I have no memory of being particularly concerned about turbulence. I even flew all the way to the UK and back without being worried.
Okay, so I have established that there was a time I didn't worry. Hold that thought.
Then I think back to those times when I did experience bad turbulence. I know when it started - flying back from NZ and the seatbelt lights were illuminated mid-flight with a warning from the pilot. I remember flying so many times between Sydney and Canberra, a short trip of maybe 25 minutes airborne, yet so often bumpy. It got to the point where I once caught a bus back rather than catch my flight. But one day I did arrive at the airport in Canberra to see a storm approaching. And we duly took off right into the storm front. It was terribly bumpy, but I survived it and subsequent episodes of bad turbulence.
So there's the knowledge that you can experience bad turbulence, yet have a pleasant remainder of the flight. Visualise that too. Think about all the wonderful flights you have had.
There was a time when the seatbelt light seemed to go on every flight. Then it seemed that there were a couple of years when the flights were smooth. Then in the last 12 months we were skirting typhoons, cyclones and weatherfronts and even the aviation authority noticed that turbulence was bad around Sydney. Then these Qantas flights were pretty smooth again. In other words, just because you have had bad experiences doesn't mean that every flight will be the same. Fly with hope.
Finally, follow what steps you can to make your flight as comfortable as possible. Try to book seats just forward of or over the wing - near the centre of gravity. These are the most stable. Try to avoid, until your confidence rebuilds, flights at times of day or year when turbulence is likely to be worst - eg storm season. You can try looking at maps on places like Turbulence Forecast and this wind map, but they often generate false fears. Fly during the day so you can look out the window. Sure clear air turbulence is difficult to predict, but in my experience most bumps come from flying through cloud (especially high cloud on long-haul) so understanding why the aircraft is shaking can help, especially if you can see the clear sky coming up!
And if your anxiety is too strong do see a psychologist because anxiety attacks are a real condition which some people close to me have suffered and one that can be treated with a variety of techniques.