The first thing to understand about the Malkavians is that they are crazy.
The second thing to understand about the Malkavians is that they are not stupid.
Do not patronize them. Do not pretend to see things that you dont, trying to play along. They will know you are lying and react poorly to you. Many say there is no way to manipulate a Malkavian. This is not the case. Malkavians are often lost and childlike. If they put their trust in you, you can tell them to do almost anything, and they will try. How, you ask, can you get that trust? I dont have a single clue. But if you get it, use it before it goes away, or just accept it this once and let it slide, hoping that it might come back.
Others believe themselves to be as mercenary as the Giovanni - pay them off in tinfoil and bits of string (Dont forget to bargain with them. Illusions are very important to the Malkavians. Heck, let them prank you once or twice, if its nothing violent. Laugh it up, or get really incensed over it, whichever they expect.)
If you get a Malkavian in a state where you think they might do something you want, consider what you want them to do. You wouldnt send a Toreador to clean out a nest of Sabbat. Youd send some Gangrel and maybe a Tremere. Just the same, you wouldnt send a Malkavian to do something like receive a visiting elder or take a message to the Justicar. Think back to all your plans that went awry because of Malkavians. What did they do? What they do best - spread chaos, mayhem and madness. Siccing a Malkavian on a plot is the easiest, simplest and surest way of complicating it and introducing elements that the plotter(s) probably didnt think of.