Suggestions?

Yup..... get the slop out of your connections. Sloppy connections is the cause of most flutter. Put one hand on the servo arm and hold it still. With the other hand, try to move the surface that's connected to that servo. If you can feel movement, find out why and get rid of it. Replace the horns or arms or clevis or whatever it takes.

As for learning how to fly maneuvers, there are a couple of good books that cover that. It's a subject that really takes a book to cover all the knowledge you're going to need to know. Model Airplane News publishes one. Tower sells it, I think. It's advertised in the back of MAN magazines.

It gives advice starting with "slop in your connections causes flutter......"