Build: http://us.battle.net/d3/en/calculator/demon-hunter#aZdckg!bYe!ZabZZY
Let me explain the skills. Vault with Tumble: Self explanatory. You could switch out Tumble with something like Trail of Cinders, since we won't be using much Disipline in this build.
Rapid Fire with Web Shot: Deals crazy amounts of single target damage. Web shot is recommended.
Sentry with Vigilent Watcher: I'm not sure for this one, but it has helped me alot through bosses. Vigiliant watched is because the bosses go by so quickly on medium MPs. You could try Chain of Torment or Guardian turret.
Shadow Power with Gloom: Pretty self explanatory. Low on health? Pop this. Gloom is recommended.
HA with Cinder Arrows: Crazy amounts of Single target here. Works like a charm.
Impale with Chemical Burn: Seriously, this is one of the best single target skills. Deal tons of weapon damage instantly, with a DoT afterwards? Perfect.
Passive skills are self explanatory. You could switch steady aim if you're mostly for close combat.
Altough, I am only level 52. This works best for me right now, and got me through the game. If you're under 51: Switch Shadow Power with Caltrops with Torturous ground.
Got any questions? Feel free to leave them in the comments.