Well I thought that most of it was self explanatory. But here goes:
AP = Ability power
MP = Magic penetration
HP = Health
Runes: The runes have two things in mind, AP and MP, and an attempt to balance the two. After having read some threads about AP contra MP I have come up with this. AP is effective in the start of the game, and can give you the early kills. Magic penetration is good midd to late game. Where the 30 extra AP from your runes isn’t much of your total AP if you have 350+.
Masteries: Well the focus here is to have these four masteries maxed: Archmage’s Savvy, Sorcery, Archaic Knowledge and Havoc. As all these boost the effectiveness of your main damage spell; Reckoning.
Spells: Clarity + Ignite. Clarity is for mana, dooh  Well I find that especially in the early game that I lack mana, and therefore have brought it (in a boosted version) to also mates midd and late game. Ignite is more personal preference as I guess it just as well could have been exhaust.
Items: I rush Mejai’s first, because you might as well start building those stacks right away. Boots, well 20 MP, enough said. Guinsoo's Rageblade just goes great with Righteous Fury. From there I go Rod of Ages for AP, HP and mana. Haunting Guise for HP and MP. And the last item is Abyssal Sceptre, for AP and MP.

You should go deeper into why you would choose the items you have and stuff like that. More details! :)