How to crossover non-neighboring strings on the violin?

1. Why does my bow keep touching the other strings?
2. Why do I keep hitting other strings on violin?

Why does my bow keep touching the other strings?

It sounds like the plane of your bow is changing as you play, causing you to hit other strings. Think of it like this: each string has its own plane or level, and your elbow controls the string level that your bow is playing on. (Whereas the forearm and wrist drive the up/down bow motion.)

Why do I keep hitting other strings on violin?

Nr 1 reason for hitting other strings on the violin is that you don't know the right arm position per string throughout the whole bow stroke.