Use your Malephic Vision on the minions to farm, but make sure they all have low enough health for a transfer. After you get a kill (Usually at level 6 when you do all 4 abilities on the guy) get a catalyst and your gonna be all good for mana and health. =D

Edit (19-05-12) : I think you guys can understand the way I build Malzahar. Its not that complicated. Your job is to burst everyone down, from the squishier to the tankier champions. Malzahar is one of the best farmers if you can use your Malephic Vision on the minions and chain-kill the minions with it, give yourself mana.