The way I cope with turbulence is by leaving my seatbelt on all the time, and if it happens - enjoy it. So many flights are dull as ditchwater - twelve hours stuck on a giant coach without even a break at a Little Chef - that a bit of funfair is more than welcome. An absolute belief in statistics, engineering and pilots helps too, with the emphasis on statistics - even though things go wrong and people make mistakes, you only have to look out of the window while taxiing at LHR to see just how huge the industry is and how many things don't go wrong. When they do, it won't be to you (same attitude means I don't get fazed by terrorism, which means it doesn't work on me. Result. And if I'm wrong, so what?).
Other times when I've been reminded about how well the machine works have been at a party in the roof bar at the Park Lane Hilton. It was a clear evening, and the approach to LHR looked like a necklace strung with diamonds shining against the dark sky. I took a moment to think about how many thousands of people were in that queue, where they had all come from that day, and how truly inconceivably complex was the thing called global aviation that delivered them. And it all hung on trust - if we couldn't do it safely, we couldn't have done it at all.
Then again, I was hiding in my rural Swedish retreat earlier this year (where I flee when I want to do some real work) and tuned in HF North Atlantic ATC for a bit of atmosphere. Every three minutes or so, Gander VOLMET warned of 'severe turbulence' for a 20,000' tall, 500 square mile chunk of mid-ocean air. Not that there was anything could have done to have avoided it. I don't know how many people got caught up in that, but it was just another night in the business. Nobody got into trouble. Wish I'd been there. Could have done the full Slim Pickins back-of-the-bomb 'Yeee-HAW!'.
None of this helps if you can't shake the fear, which is when to take yourself off to the professionals. That's worked for me (not in this context), although it helps if you can get a good word of mouth recommendation from someone who's been there.
R