Anything that can give you advantage on attack rolls. Attack from stealth, blind opponents etc. I would activate sharpshooter whenever I am 70% or better to hit with it.
Gloves of Archery gives a straight +2 to all ranged attack rolls and are good in Act 1 and 2 and can be obtained from the vendor at the Goblin Camp. You can also go with Crossbow Expert and Gloves of the Groveling Underdog to have permanent advantage whenever you are fighting multiple enemies at melee range.
Acid can be used to lower the AC of tough opponents and increase your chance to hit them with Sharpshooter.
Some melee weapons will lower your crit threshold even if you are using your ranged weapons. Lowering your crit chance is great when you are spamming lots of attacks with advantage, just going from 20 to 19 will see it happen so much more frequently.
