Start red buff, move to raptors, then wolves to blue to gromp. Take scuttle then look to gank, invade, or skirmish. back with at least 1k gold so you end up with a stalker's blade and a long sword.
The basic burst combo for champions and minions alike is to get in range, throw your ranged auto, then e immediately afterwards, q, aa, then the second part of your q should hit and continue attacking if the opponent isn't dead by then. If you need extra damage throw in an r tap to knock them up and keep them in place for more aa and q damage. Don't waste your w on camps, and save it if you're facing an enemy jungle such as rengar with a vital dash. If you're ganking it's wise to use it for the movement speed to get as close as possible as fast as possible.
The damage from the explained combo will be ridiculous by the time you finish your core items because duskblade will activate and if you e them right after you auto triforce will also proc. Electrocute and extra q's (lategame q cd is 2.4 seconds) should finish them off if they aren't dead by then.

If you need help on what to build, cater your boots towards the enemy team's damage. If you're taking too much damage in fights, build defensive items to compensate for it. Whether you're behind or ahead death's dance and sterak's are never bad items, which is why they are listed in my favorite build.