Malzahar is a very good mage, he excels at mid/solo top. He can also duo-bot lane, Malzahar takes a few rounds to get the hang of, on this build I will detail the Items, Runes, Masteries and How to Lane as Malz.

I take Magic Pen Marks, Mana Regen Seals, CD/Flat AP Glyphs and MS/AP Quints, this setup alows Malz to control his lane and do great damage.

I take 9/0/21 Masteries, this allows me to do alot of damage and have fairly low cooldowns.

I take boots and 3 pots and head mid/solo top if i was too slow to call them i go bot, I focus on last hitting until i have around 1.3k money then i go back and get my catalyst. If im doing well, i pick up a mejais, if im having difficulty I rush a Rabbadons, I always pick up my Rabbadons as 3rd-4th Item then i max my boots for Sorc's Boots. If the game is ending soon i pick up a Void Staff, but if it seems like it will go for longer i pick up a WoTA.

This skill sequence i find is the most effective, if your team is ganking more you may want call of the void leveled first.

Pros:
Good Damage
Dominates when fed
Good harass
Godly at last hitting creeps.

Cons:
Squishy
Often Targeted
Slow get-away

I think Malz is a great mage and is very easy to learn, this is just my opinion on how to play him, im not a 2.3k elo but i do well with this build.

If you downvote atleast say why.