I Know how you feel because I used to get scared to go on rides, but now I am okay and I feel like I can go on anything.
However if I am scared, when I watch the ride I am hoping to bravely go on, I tend to watch one person and see how fast they move, their reaction and how they feel after coming off.
This makes me feel a lot better and I always find that once I have sat down and been strapped in, I feel very safe and ready to ride!
Hope this helps