I'm going to try to keep this short and to the point. Malzahar is my current favorite champion to play and when played right, can disrupt a whole team. His ap ratios are actually really good and he is a nuke mixed with damage over time.

Pros:
-Sustainability
-good spell pen.
-Great cc with his q, and ult
Cons:
-Squishy until you get spell vamp
-Have to worry about positioning in fights

One of the main things I see is people rushing arch angels. What I like to do is let the mana build up, then finish it later in the game. So if you can buy other items before arch angels staff I would highly suggest it.

I didn't put much Ap in the runes because it's far less efficient late game than magic pen is is. Late game magic pen quints and marks should help early game as well.

I really suggest less harassment early game and more farm with his e. That being said when the opportunity comes, don't be afraid to silence your opponent, just don't spam your q, it will just burn mana. Try hitting creep waves when they are low on health by a turret with his e. This will help you get mana back early game and end game.

For a combo i usually do w,e,r. Hitting the q is sometimes difficult to do so i usually use that as a finisher if the main combo doesn't finish them off. Also target the champions who can disrupt your ult. You don't want to be in the middle of an ult and then die because you were thrown or stunned.

I suggest running ignite and flash so late game health regen won't stop you from killing the enemy. Flash is for getting out of situations where you may have over extended. I also would say run with exhaust flash if you don't want ignite.

This is my first guide so please be nice with the comments haha. If yo have any suggestions as to how i can make it better feel free to let me know, because I'm sure there's a lot of room for improvement. :)