Early Game (lvl 1-6)

I start off with Call of the Void as my first ability. Although Malefic Visions is the theme of this build and my favorite of his abilities, at level 1 it lacks any extra damage from AP and is very hard to push through minions. Call of the Void can be spammed at the healing pad to work on summoning the Voidling before going to your lane. Call of the Void can also be used to check bushes instead of having to face check.
Early game I try not to do anything too risky. If you see an opportunity for an Ingite + MV to get a kill, go for it but you have to be fast about it. Doing this can result in good early game kills/assists. Also remember that your autoattack does a fair amount of damage when every one is low level, so throw that in when you try for a kill.

Next I get 2 MVs, by the 2nd one, you should be constantly pushing MV through minions and trying to get it to bounce onto people's faces. Remember to place your CotV behind enemies to keep them harassed, but pay attention to your own safety. Next level I get Null Zone, it's good to have at least 1 level in NZ in case there is an emergency and you need it. It is a good scaring ability and is needed to accompany Nether Grasp, which you get at level 6 of course.

Mid Game (lvl 7-13)

At level 7 I pick up another CotV so that it continues to put out good damage. I then alternate between MV and CotV until MV is lvl 5. If the enemy team is very tanky, you may need to upgrade your Null Zone sooner.

Some mid game tactics include: If you find your self being chased and you know that there is no way out, if the enemy is squishy enough, you may be able to turn it around on them. If the enemy is a melee, put NZ under you and use CotV right infront of you where they are attacking you. Put MV on them as well, possibly Ignite too. When some one sees you using alot of abilities, it might scare them off. The best way to turn something around on some one is to let the enemy chase you to a bush. When you reach the bush, be ready with CotV. Silence them, NZ them, MV and NG if you can. This is an amazing way to nuke some one out of their own carelessness. It is normally harder to nuke some one if they see you coming, but this bush tactic works almost all the time.

In team fights, try your hardest to have a golem buff. I usually go for it around lvl 9 or 10. When you have the blue buff on you, you can put out loads of spells druing team fights. Look for easy targets, squishies, or groups of enemies to use CotV on. It is also good to use on their casters so they are silenced. Whenever you see a group engage in melee, place a NZ down under them. Remember to use your NG on a priority target, or if you need it to save yourself. MV is best used on enemies that are about to die, so that it bounces off them and can continue through other enemies. MV is also good to use when enemy creep waves arrive so that you can get some mana back if you are low. As for positioning yourself, remember that Malzahar is very squishy and lacks a good escape ability. Try to stay behind your team mates, be ready to Flash out of danger if you feel threatened.

Late Game (lvl 14-18)

Malzahar shines the most during late game, but only if you use him properly.

You should be getting your final few items now. Your AP should be very high so your abilities will be hitting very hard. Because Null Zone is most effective late game, you will be leveling it up through your last levels until 18.

By late game, it is important that your soulstealer is stacked decently high (13-20). If the stacking is not going well, you should consider selling it and buying somthing else that gives AP. You should have a good bit of cool down reduction by now, especially if you continue to get the blue buff. Use your nuke combo to dominate squishies that get too close, or use it when a carry attacks you (remember however that olaf's ultimate will cause him to be unaffected by your stun, however the ult will still deal damage). Stay safe near the rest of your team mates, Malzahar is easily focused and killed. If you have your Quicksilver Sash, save it for when they enemy team tries to focus you. Lets say ashe shoots her ult at you, use QSS the instant that it hits you and run back. However if ash continues to attack you and you are too slowed to get away, your only option is to turn around and fight her. Squishies fall incredibly easily to malz late game. One CotV will deal over 50% of their hp if you have enough AP. And remember even if you do die, if you remembered to put MV on them, you could still get the kill, and since the kill would be after your death, you would gain 2 stacks, even if you lost some for dieing.

When the enemy tank gets set up in a spot and starts tanking, the best way to grind him down is a Null Zone. While your allies may be slowling picking at his HP, Null Zone will deal % damage, and although it is lessened by Magic Resistance, it will take the tank's HP down very quickly compared to other forms of damage. If you see some one such as Nunu or Galio using their ultimate, if you are not caught in the taunt, one well placed CotV will end their ult immediately. Also remember that CotV can reveal areas, so if you suspect a gank, cast it over a wall and you will get a good view of where you use it.

If the opposing team is attacking the Baron, this is an opportunity to deal massive damage since they are all crowded around the Baron. However do not be the first person to attack, you can get focused and killed instantly. Wait for a tank or some one that can absorb damage to go into their group, then throw out your AOE attacks, you can also try to steal the Baron. If your team is not willing to attack the Baron, lets say that they are seen attacking it but you are in the jungle above them, position yourself along the ridge behind the baron and wait for a good opportunity. When the time is right, use CotV to reveal the Baron's hp and the enemy team, use NZ to deal damage to the Baron and cast MV on the Baron. If you are successful, you can snatch the Baron for your team and leave your enemies enraged. Another good time to use CotV over a wall is to catch a turret hugger that is very deep, you can use it through the wall to hurt them, and then try to MV them. If there is a 5v5 and the enemy team is hugging a turret, snipe them with CotV and bounce MV off minions to keep them harassed, and possibly create an opportunity for a tower dive. If some one strays too far from the turret towards your team, do not hesitate to nuke them down, as it may be your only opportunity for a kill for a while. Your ult should have about a 48 second CD at lvl 18, so use it frequently.