the runes have 11 mana reg per 5 sec so don't over use your spells.
(if you run out of mana use clarety.)

Okay, sear is really high dmg spell good if you are in a lane with one ragen and one mele. if it is 2 mele start with pillar of flame. remeber that blaze puts a dot that takes like 22-26 hp in dot.

Here is a little thing I descoverd.
Check your map where your creeps are whne you have ultimate and try to hit the person with low hp when your creeps are kinda near tower. that will result that: your cast your ult hit the guy with low hp bus he is still up and running, but he dosen't know that his creeps is behind him and your ult will bounce and bounce back on him wich kills him. ( best for mid )

Mana prob: The runes is very helpfull and Arch angel will boost your ap and mana reg, don't overdue spells.

Items:
Rabbadon buffs your ap and gives 155 ap witch will buff the Artch angel whom gives you even more ap trough your mana. rod of ages is great and stacks on kills/creep kills ( ap/hp/mana ). merajs shoul stealer you get a lot of ap witch gets buffed buy rabbadon. death fire grasp i'ts like a 7th spell good vs tanks and 1 0 1 when you don't want to waste your ult.

sorry for my gramma, but im just putting this out.