A real good inspection of the plane beginning in the building stages will prevent flutter. As you progress through any build, you're constantly scrutinizing your work against several pitfalls..one of which is potential flutter. If you have solid goals for the plane to begin with [fast, slow, 3D, etc.] then you'll be better able to set the plane up accordingly.

There are areodynamic considerations, structural considerations and linkage considerations already covered here. The controls need to be tested against manual pressure and the control surfaces need to be operated against manual pressure to see if they are stiff enough. In some cases you need to either fiberglass the control surface or add another linkage/control point.
Take the time to see how "flexxy or twisty" this stuff is before you find out later at the field.

If the servos are hooked up with the best mechanical advantage [linkage geometry], then that will go a long way to help limit [postpone] flutter. Unless you are flying 3D, it takes very little aileron movement to control a high speed plane. Using the inner hole at the servo arm and being about an inch up on the control horn end will give the best mechanical advantage [leverage] and control resolution.