Malzahar is a very strong burst out dmg champion, if played properly he should often carry his team. I play Malzahar always in the mid lane YES it's a big deal - you need the gold - you need the exp to carry your team and get lots of kills

pros:
strong burst out dmg
can kill tanks very fast
very usefull in team fights
easy to control mid lane

Cons:
Squishy
Has no escape ability
can be ganked easily
targeted in team fights

Greater Marks of Insight: Magic penetration is really important, with the marks - mastreies and boots you will have about 43 magic penetration

Greater Seal of Replenishment: You see I got them flat because you will only need them at early game, when you are a bit higher you should start getting golem buff

Greater Glyph of Celerity: CDR though you don't need much CDR the glyphs are usefull mid and late game

Greater Quintessence of Fortitude: Malzahar is very squishy early game

Summon Voidling: Really usefull, first it distracts enemys for some reason, second it helps alot with farming

Call of the Void: Some might ask why I had only one point in lvl 2 and then left it, well the reason is because it costs lots of mana, it's good harrasment but very hard to use in 1v1 if your target is moving because it only hits full damage if the target stayed in the middle of it though the silence is pretty nice in 1v1 and team fights

Null Zone: The Anti-tank skill, if this skill is used properly with Malefic Visions, ignite and ult It's a sure kill

Malefic Visions: This is my favorite skill, it has strong damage it gets your mana back, very good for farming and good to have last hits to get the kill

Nether Grasp (ULT): One of the best ults, As I said in Null zone you can get lots of free kills, in team fights try to target there carry or there highest damage dealer (Twitch - Lux - Jax.....)

This is pretty obviouse...

Ignite: to get the kill or put it on champions that have life steal or heal (Swain - Warwick - Soraka....)

Flash: The best summoners spell always gets you out of sticky situations

Other good summner spells:
Teleport: best summoner spell for farming
Cleanse: Good to remove stuns and some debuffs - has low CD
Heal: if you just started playing with malzahar and feel its hard to survive
Ghost: good for escape, I just prefer flash

Summoner spells you should NOT Take
Clarity: You have the mana regen runes, Malefic Visions gets your mana back, when you are a bit higher lvl you should get the golem, won't be used at all
Revive: NO NO NO, I don't know why they made this summoner spell

First get a doran's ring and a health pot and go to the mid lane, always call mid at the champion selection so no ashe or sivir or any other champion opens his/her mouth.
Try to put Malefic Visions and ignite on him, that should take about 40% of his health and will make him use his pot.
When the minions start showing up, Just play safe and farm, you will get the chance to kill him later on, now you will only focus on getting the gold.
When you get to lvl 6 you should be able to kill him, put Malefic Visions ignite try to land null zone on him and fastly use nether grasp (ULT) if he isn't dead just put another Malefic Visions or hit him with call of the void

after this go back and buy the boots, return to the mid and start farming again, once your ult is back try to kill him, don't hurry though you might die because of that, make him push a little bit and make your move quick, if you killed him again and you are lvl 9 look in the other lanes and try to communicate with your teammates to make a successful gank, the tower should be easily down because your opponent is lower lvl than you and dead a lot.

By this time of the game you should have already got more than 1600 gold get the needlessly large rod, some might ask why I get this before the soulstealer, well if you got it you should have about 75 ability power, with the soulstealer and no stacks you will have 95 wich will make kills very easy, getting Rabadon's Deathcap (THE HAT) shouldn't take a long time

End game starts now, you have a good amount of kills and nice items team fights will be starting to show always try to use call of the void in the middle of them it will silence, putting Null Zone in the tanks places will get them killed fast, use the ult on there highest damage dealer, by that they shouldn't be a big problem if your team did there job

Zhonya's Hourglass is the last core item, after this if the game lasted long enough there are 3 items you should start thinking wich of them to get
Banshee's Veil if the oppenent team had a karthus or has lots of casters
Thornmail if the opponent team had auto attacks (Trandymere - Master Yi - Ashe)
Void staff if they start getting some magic resistance items

At the end I hope you will get lots of kills with the guide and have fun playing the champion.
make sure to comment, ask questions and vote.
Thanks for reading :D