Hey, I'm SpicyCheeseStick, and I main Veigar mid. He is a very interesting champion, with high nuking capabilities. There is a lot to cover, so bear with me.

I prefer flat runes over scaling because you need a good early game, so flat runes are more effective. You don't need to much help from runes later on, because you are so nukey.

Man, go 21-9. I give Veigar the Max damage output possible, while keeping him healthy during early laning phase.

OK, this takes Alot of time to master. First of all, Master landing E. You need to know how to perfectly land without fail, and this comes with practice. Early game, just harrass with your Q.
YOU NEED TO SEND OUT YOUR WHOLE COMBO IN LESS THAN ONE SECOND
With Deathfire Grasp and Ult
E-DF-R-W-Q
With no Ult
E-W-Q
With Ult, Against AP Champs
E-R-W-Q

BALEFUL STRIKE (Q)
Use this skill to farm and harrass. You should prioritize farming because the gives you free AP! This means that you should keep farming that Q, wherever and whenever. I aim for 100 extra AP at

DARK MATTER (W)
This is your nuke. Late game, it can take away half of a person's hp bar. This is great for farming too, if you have farmed your Q well enough. This is a main part of your burst, so use it wisely

EVENT HORIZON (E)
You will need to know this skill in and out. This is your only escape, so master it well. Know when to immediately stun the opponent or when to trap him for a while. Practice Makes Perfect

PRIMORDIAL BURST (R)
Holy ****, this is one of the best ults in the game. Late game, it does 1500 flat Ap. Alos, it deal 80% of your targets AP. Super OP. One hit Squishies, and win teamfights. 2 stronk.