there isn't really much to know about graves, that you won't learn playing another ranged AD.
the main differences that set graves aside from the other AD's, however, are his abilities.

Buckshot: This is the first skill you max, it has a high damage output at an range, it's useful for pushing, and if the enemy comes close, you can really make them hurt.
Quick Draw: This is a good tool for positioning, and a free boost to attack speed. this skill almost eliminates the need to buy attack speed items on graves. You should be using quick draw to position yourself for buckshot, to catch up to a retreating enemy, or to increase your damage output in a certain situation.
One thing you should remember, is to keep quick draw available as an escape ability, for when you get attacked. don't use it against minions.
Smoke screen is useful as an escape, and, coupled with quick draw, and initiate.
When you hit someone with smoke-screen, they will only be able t see the units and champions within the bubble, leaving them open to attack.
keep in mind, however, that units attacking from outside the bubble will be revealed.
use it to set up ganks, and to slow an advancing enemy(fire it in-front of them, not on them). using this on minions is a waste, don't do it.
Collateral Damage: This is pretty much the most 'balanced' ability you have.
you can really use it to turn the tides in a team-fight, or as a high damage/high range nuke in lane. the ability is pretty self explanatory, but in a team-fight, you want to hit the enemy in-front of the rest of their team. It has a high base damage, and a high scaling with your bonus damage.

with high crit, you should be dealing a very high damage, and you should be getting a high level of survivability with the stacks of True Grit. (40 free armor and mr, at later levels)