I've been flying professionally since I was a teenager. I skydive, and fly airplanes ranging from low level types of operations, very close to the ground and in the mountains, to high altitude large and small turbojets. I don't like heights. I never have.
Find something to take your mind off the idea that you're high above the ground. You probably have little fear of riding in a car. In a car, the bottom of the car is just beneath your feet. In an airplane, it's no different. The floor of the airplane isn't thousands of feet beneath you, but directly below your seat. You're not high up at all, but sitting in a seat, no different than in your home or in a car. Concentrate on that.
Take something to read. If I'm not sitting in the cockpit, I either read, or sleep when I travel. I don't enjoy sitting for any period of time without something to do, so I study, read, or sleep when I'm going from one place to another.
Turbulence can be upsetting, but if you've been on a boat on a river, then you understand turbulence. If you've been in a car on a rough dirt road, you understand turbulence. As an airplane moves through air, it may do so smoothly, or with a few bumps, these are no different than an uneven road or the swirls and turbulence found in a river or on the ocean. The airplane isn't going to fall or become uncontrollable, it's just a little bouncy. If you can tolerate it in a car, you can tolerate it in the airplane. No difference, really.
Some people find that eating in advance helps, some find that going without eating helps. Find out what works for you. If you can keep fresh air flowing over you by using the overhead vent, you may find this calming and some relief to any airsickness or uneasiness you might feel.
I find that sitting by a window helps most people. I much prefer to sit by a window. It's less convenient if you need to get up to go to the toilet, but I like to look out the window. I feel like I'm in a big tube with no sense of up or down if I sit near the aisle. Window seats help. Being able to look at a distant point and reduce the sensation of motion helps.
Personally, turbulence and bumps tend to rock me to sleep. Try it a little and you might find it works for you, too.