So first build, and i have tendency of miss spelling so let me know. First, Malza is my main and with this build, it is good for all, pros and noobs alike.

Magic pen for marks. do i need to explain...

Seal runes, I prefer flat health runes to mana regen runes for Malzahar because Visions gives so much mana every creep kill, that it`s not necessary, but still optional. heath runes will help early game survivability.

Glyphs are all about flat AP, this will make visions do so much more damage potential.

quints of AP is same reason as glyphs.

Masteries are same for basically all mages.

Ghost can be used if your not use to flash.

so first off, this build is good for mid or laneing. So to begin with, meki pendant and mana/health pot to begin. optional is 2 mana pots.

The fist thing you need to do is gather enough cash to buy tear of goddess, and some boots, if possible lucidity boots, but be sure that you want tear of goddess to start stacking early game. this will provide good mana and mana regen for the rest of laning till you get Rylai`s Scepter. Rylai is kinda big build so return to base i need be, to get some AP.

Once you have rylai`s, archangel staff is next. this will resolve all your mana probs if ever there was any, and boost you AP. from there, Rabadon`s death cap. once you are a this point, your items depend on your opponents team. If they have a big magic res team, then Void Staff, and abyssal scepter combo will destroy tanks. but usually go for flat AP, even going as far as buying plenty of Rabadon`s Deathcaps.(that will boost your AP to off the charts.

If you feel very squishy, getting Rod of Ages is not forbidden, but get it after Rylai, or archangel to give it time to stack.

Overall, Malza is a great pusher, harasser. Void Gate is spell #1. use it to check bush before entering if laneing. Great spell for harassing squishes and mages because of silence. Then malefic visions is to be maxed out ASAP!!! before casting visions on a minion, be sure to weaken it with basic attack so the spell can the kill minion for mana regen. Last hitting is not recommended/needed for malza in my opinion. Be sure to harass with Gate at enemy tower so they can`t collect cash. Also be sure to have null zone lvl 1 before lvl 6.

Throughout the game, carry or not, you should be always killing waves of minions between team fights(to regain mana). Clearing them with all 3 of your spells at once(if low on mana just malefic visions should do) mainly try lining up the gate to hit as many mage minions and null zone on melee . Malefic visions should be bouncing around for the whole wave.

Like all mages you stay behind the tanks and others occasionally going in front to spam your spells.

Role in team fights
#1 YOU are the enemy minions remover. Doing a drive by spell mostly gets the job done.

#2 Use your Rylai`s slowing ability to slow squishes for concentration attacks by your team. and also slow backing enemy team.

#3 If your team has no or little stuns/slows or to short range or what ever, you must some times go and cast ult on a squishy that pops out from the front lines.

#4 harassing in team fight is your specialty, crowd control, and visions. use visions all the time and try to concentrate on single target(mostly squishy). Harassing tanks once in a while also helps. Making a tank feel Squishy will make him make mistakes. Capitalize on that.

#5 Saving you allies with your crowd control. Void gate silences, and null zone damages the enemy without realizing, or separates fearful champs. your ult is also good for protection of teammates, BUT beware, it is your greatest and most dangerous spell!!! you are vulnerable, so make sure to have team beside or in front of you.

Situation 1, You are ganker solo

The killer combo for Malzahar. Always use ult when target is on Null Zone. try placing null zone in front of target direction (hoping he goes in middle while ya cast all your spells), simultaneously cast gate on target. Visions is very important to cast after, because of damage/range. Why range? Ignite has simulator range to visions, and therefor once ya pop your ult, ignite target. this will prevent interrupting your ult.
If target does not die, and is low on health. the target is slowed by rylai, so chase(preferably do not auto attack, but that depends on health left). All your cooldowns should be almost over, simply cast.

situation 2
you are being ganked by someone alone or 2
Immediately cast null zone under yourself, and the rest is same as the gank. If multiple targets, choose the one that with most potential of dieing, lol. Take 1 or more down with you, muhahaha.