People often forget about the importance of the bow because they're so busy thinking about the violin, but actually a good bow can make an enormous difference to your violin playing and really help you to get the most from your violin. Choose a bow to match your violin (So it's a good idea to start by looking for the violin and then try and look for the bow afterwards.
Balance is important. Does it shake? Do you feel well-balanced when the bow is playing. Is it too heavy or is it too light for you.
And off-the-string playing: does it bounce and work well off the string? If you're a beginner you really don't need to worry too much about this. This is more for advanced players. As a beginner you can just start with whichever bow comes in your beginner violin outfit but make sure that it is decently haired and is not wound too much in the wrong direction.