I always like to have about four feet of the tree trunk left. It gives a lot more leverage, so you don't have to work the machine as hard. Sometimes somebody's already cut them as close to the ground as possible though.
Different kinds of tree have different root systems. Pine, for instance are pretty shallow-rooted and pop out pretty easily. Elm trees are really tough--they have a big tap root that runs pretty deep right in the center, and the wood is pretty stringy. For stumps in general, I just try to dig as far around them as possible, cutting as many roots as possible, then get the bucket teeth under there someplace and try to pry them out. Sometimes you have to move back and forth from one side to another and get them a little loose here, and a little looser there, until they pop out.
Keep in mind that if you grab with one side of the bucket or the other (which you probably will do), it puts a lot of twisting stress on the machine. Most machines have enough strength to break, or at least bend themselves if you get them in a situation where you're concentrating all their power on one component (like the far lefthand tooth of the bucket). Yours is probably no exception.
Something else to watch out for is that when you succeed in breaking a root, dirt will fly. More than once I've almost been beaned by a fist sized chunk of mud.
One more thing--just because there's a tree stump there does not mean there's nothing else there. Once, a long time ago, a homeowner asked me to take out a stump and I took out his gas service line along with it. :Banghead
So keep the glass closed and maybe break the glass
