Note:

Since your not the jungler you will need a regen item I recommend philosophers stone since it increases your income compared to catalyst that costs 500 more gold at the begining and does not give gold .

The haunted mask will give you at the beginning the ability to take out anybody. As soon as you get it gank some lanes.

The malady will give you the ability to kill the tanks fast ,don't be scared to take them out.

Use shurelias to cast your Q over your ennemy ( he will fall right on it) then use your R and your W, use your E as soon as he escapes then cast anither Q and. R ( 2x R if needed).

The E can be used to counter some champion's main spells. For example Katarina.
you can use E also to carry your enemy throught the minions at lvl 3-5 combo (flash + E carries well)

Enjoy :-)