Malzahar is an extremely potent champion, very usefull in team fights and deals massive damage. His strong side is to single out enemies as they come, focusing them down one at the time.

Malzahar is super easy to farm with, Just use Malefic visions on a creep and kill them one at the time, also restoring your mana spent on the skill. One of the problems at start is when your Malefic visions jump to the siege creeps, making it alot harder to regain the mana. On big creep waves you can kill pretty much all the Mage creeps with Call of the Void

In team fights you should stay in the background and send Call of the Void on as many enemies as possible. Use Malefic Visions on the champion being focused by team, and use Nether Grasp on the crowd control champions such as Janna/Sona/Soraka or Veigar (just examples for champions easily killed with Nether Grasp or good to disable). Use Null Zone on as many enemies as possible to drain their health down.

Pros
: Extremely potent versus single targets
: Very valuable team asset
: Easy to gank with

Cons
: Dies easy if focused
: No escape skills