I would add that you need to learn to better start the string vibrating. I almost said I never think of weighting the bow but that's not entirely true. The bow needs very little weight to get a string vibrating if your technique is good. Place the bow at the tip on the g string. Weight the bow normally, just a bit of arm weight. Wiggle the string ever so slightly back and for, by that I mean just a tiny bit, notice the bow grabbing the string. Do not let the bow start the string, just 'grab' the string with the bow and move it back and forth a little to feel the grip of the bow. The string should bend slightly in the direction you're pulling or pushing the bow. Then, in the most relaxed way you can muster, RELEASE the string and begin drawing your bow towards the frog. Do this many times. Place bow on string at tip, wiggle a little bit to solidify the bows 'grab' of the string, no sound yet!, then RELEASE the string and draw a big relaxed sound out of the full length of the bow. I alternate the position, tip, middle, frog and direction to feel the different weight needed for different parts of the bow and the different strings engaged.