Penetration is a good damage boosting mechanic in general. Off the top of my head, for a 4-link, which is what you should probably be looking to have given where you are, I'd probably go with Ice Shot - Barrage/GMP - Elemental Damage with Attacks - Cold Pen, unless you're going Raider for your Ascendancy, in which case the flat damage Ice Bite gives from your Frenzy Charges probably pushes it above one of the other supports there.
One other thing that comes to mind that I dunno if you know about is the recipe for a +damage magic weapon: a weapon, a blacksmith's whetstone and a magic or rare Rustic Sash gives you that weapon back with a guaranteed damage modifier. If the sash is rare, the modifier is 50-69% increased damage. It's a really good way to keep your weapon up-to-date while leveling - every 10 or so levels, get a better base bow, then do the recipe on it (then, if you want, you can also Aug it for a second random mod).