How do I properly adjust my shifter cables on my bicycle?

I have a 24 speed mountain bike. It is a rather nice Diamondback and I will most likely take it to the bike shop once a month for adjustment but if I am in the trail and it is slipping what is the best way to adjust it? For example today my 3,4,5,6 gears on my back wheel would slip down. Any advice?How do I properly adjust my shifter cables on my bicycle?Here's the place to find that and much more: sheldonbrown.comHow do I properly adjust my shifter cables on my bicycle?Buy a bike without gears...trust me they are more trouble and less fun!!!!! BMX bikes are the ones to have! Diamondback is a great name, look into the Diamondback Joker!!!!!