The sight reduction of Smokescreen has great utility, along with the AoE slow.
Smokescreen can be used to juke your enemies and allow Graves to make decisive choices when either chasing or escaping.
It can be used to set up a gank, because the target will not be able to see any incoming champions.
A Smokescreen can be a strong deterrent for an oncoming enemy team.
Smokescreen greatly diminishes the utility of an enemy champion that relies on skillshots, such as Xerath or Lux.
Graves'sQuickdraw can be used to dash through thin terrain. This allows Graves to be very mobile and can benefit him in chases and escapes.
Try to use Collateral Damage at the beginning of a teamfight when your enemies are grouped together, allowing you to hit multiple targets.
When the champion against you has a blink (eg. Ezreal), and he attempts to engage you, throw a Smokescreen to where he blinked, and quickly dash away leaving your opponent visionless.
By using smart cast, you can cast Buckshot and Quickdraw together in such a way that you dash back while shooting the three bullets of Buckshot in front of you. Use this combo to finish off enemies with low hp and make a quick escape.