About the build
My first item (sometimes before the warrior enchant) is the BT. It gives me some lifesteal, wich allows me to regen all my life in the jungle (with the machette lifesteal effect). It also give a lot of AD, wich is great on graves because his ratio are huge (1.1 on his Q).
I buy youmuu for the same reasons: AD scales great on Graves, and the AS allows him to AA a lot.
Last whisper for AD and penetration, nothing to comment.
I'm still trying the last part of my build (PD and IE), but I don't really know if critical hits scales on graves.
Of course, if the opponent team gets a lot of cc, go on mercurial scimitar, it's a great item too on graves
Start on golems, with the assistance on your team. Then, go on your wraith, and, when your smite is up, on your red.
You can gank mid at this time, or go on the blue side of your jungle.
Graves is not the best champ to gank, but he's able to deal lots of damages (especially with his Q).
Prefer the lane with some CC, or the bot lane.
When you gank bot, they will often go back through bushes. Try to apply your Q spell against a wall, to instantly deal the full damages, and burst the adc.
Graves will do lots of damages, especially at lvl 9. Try to go on drake at this time. Mid game will be where you rules, so make your targets surprised by your burst (Q-AA-Z), and take the more towers/drakes you can.
In late game, Graves gets less powerfull, but he still deals lots of AOE damages, and remember your smoke can force the opponent team to go back, because it will be your best spell in late