Machete will build into Stalker's Blade (your 1st priority as JG), 2 potions to help in case you don't have a good leash, and of course some vision.

If you got a kill before your 1st town, you may be able to go straight to warrior blade, if not get the stalkers blade and get back out there.
If you can afford it, get the upgrade and Zeal to build into your Statikk Shiv.
Statikk Shiv will help with some extra xp when you go help out in lanes for those player kills early in the game.

After Statikk Shiv, build your BoRK (blade of Ruined King), Youmuu's Ghostblade and Phantom Dancer in that order. This will get you some life steal then build your attack power before really maxing out on crit.
Late mid-game, sell your Warrior Blade and build into the Infinity Blade. Next, sell your potions (cause they are not going to do you any good anyways) and build the Trinity Force.
Finally, if you find yourself in town with a ton of gold, upgrade your trinket.

Q-W-E
W 2nd to save you a trip back to town in case you get a player kill chance.
Get your Q maxed quickly, but don't forget completely about E.
As soon as you hit 6, get your Ult (R) and watch your map for some nice kill potential.
Don't worry about W till last, once you get some life steal, it won't be that needed.