This build is MY way to play Malzahar. The only thing I recommend is to play him according to your ennemies, and once you get the hand of him try to adapt this build to play him the way you like to play him. Beethoven said "Don't only practice your art, force yourself into its secrets"... Well this is what I want you to do.

Use your DoT to clean minion waves to restore mana being careful not to push too much, otherwise you are a free kill for the enemy jungler. Do not use your AoE in early game because it will cost you a lot of mana, and it doesn't deal that much damage, unless ther eis a stun or a slow on the foe. If you place it and the walk in it for half a second it won't hurt that much.
Use your call of the void to silence enemies and hit them but note that the two portals can serve a very temporary wards. Cast in in the grass with one side inside and you will see if there is a gank coming on you.
Your ultimate is one of the most hated in the game. When your AoE reaches 13% of base hp per second and your DoT deals some 600 damage, an ultimate in the face quite guarantees a kill. try not to use it briefly and in team fights as it will stop you from moving to, making you too targeteable. If you are on the other side of the wall or behind a tank, do not hesitate !
Also try to put your DoT before casting your ult if in team fight, because if your target dies the dot will spread, whereas if you put it when he starts running he may die far away and you'd have to cast another malefic visions. Note that the first thing many people do when ulted my malzahar is flash right away in panic, so they may be out of range of a DoT.