I let an item slot free 'cause it's situational, if you wanna be a tank, you can take something like a Raduin, a Guardian Angel, a Warmog.... If you wanna be a dps, take a Last Whisper, may an Infinity...
Do never forget to take wards, and some heal pots (for the ~9first lvl, it's useless after). When you have the vampiric scepter, be sure to wait a little before kill the minions : if they've less than 15% of their health (45 for the 300 one, 60 for the 400, etc...) you deal a crit strike, so x2 lifesteal ;o
Do not use your R on your target location, she can dodge it easy. Use it in front of her, in the direction when does she go. It's better if she can't see it, so may she can stop run away. Like if you jump in the fog of war, or in the jungle near to her. If you're enough tanky, you can jump beside the ennemy, in the middle-late game, and engage the teamfight with an epic bush stun not expected by the ennemy (like if your team is around the drake, the ennemy team at the mid lane bushs, jump in the wolf bush and stun the ad carry for an amazing fight! (while dealing ton of damage on the carry, and then may kill him before the fight begin').