I really like khat. It's an unusual stimulant in that it's almost all mental and not physical but it can get speedy as hell after you've been chewing it for a while. It took me about half an hour of solid chewing to build up a good buzz so don't write it off immediately.
As for technique, I'd advise chewing it slowly with gum until you can't hold anymore, then spitting the juices out. It can be quite messy. It always left me with a crippling stomach ache as soon as I stopped, as well.
It degrades seriously quickly so I'd advise starting on it as soon as you get it. Even then there's a good chance it won't be working too well if it had to be flown to wherever you live; the khat I've tried here has been piss-weak compared to the stuff I had in east Africa. The young small red-tinted leaves are the most potent.