Try this exercise (I believe it has been suggested to me on this site elsewhere):
- set a timer for one minute
- get a camera to record yourself in such a manner that the camera is looking parallel at the violin
- start your bow at the frog as the timer starts
- continue to drag it all the way to the tip but FILL THE WHOLE MINUTE WITH ONE BOW
(you can always start with smaller increments of time -- in fact, that should be expected. The point is, long enough to make it fairly uncomfortable.)
- focus on keeping YOUR BOW STRAIGHT
- watch your video and look at where your bow is.
The main trick is to keep the bow moving straight. Try this video and observe how straight the young guy's bow moves:
Another thing is to recognize the shape of the bow arm. When the bow is at the tip, your arm should be at such an angle to the bow that it appears as an acute triangle.
When your bow is in the middle, your arm should be at a right angle to the bow, forming a square.
When your bow is at the frog, your elbow should bend so that the shape is something like a right triangle.
This will help you with control over where your bow is.
If you have any questions, or if I misunderstood your question, let me know!