Piano Forum

There are two approaches you might find helpful. The first is just to work on that section hands separate and then when you put the hands together let you brain focus on the hand that's NOT trilling. Sometimes that works fine. But if it doesn't the second approach is to write out the trill in full, in this case, the easiest thing would be to write it as b-c (two 32nd s) b - (16th). Because this trill is approached from above, I'd start it on the principal note, b. Once you've written it out, practice it very slowly to learn the coordination of the two hands. Once you've got that down, you can try going back to the first approach and relaxing a bit. As you get more comfortable you can add repetitions to the trill. And I do recommend thinking about the hand that's not trilling, somehow ornaments are  easier if you aren't thinking to hard about them.