Only had my machine for about 2 months, but here is what I have learned.
Primarily, I run sensitivity in Auto. There are times it falses a lot, and I have to turn the knob clockwise until the chatter disappears. Usually this is in the surf zone, and a sens setting of 4 to 6 will run smoothly. In the water, or completely out of the water, and you can run the sens a little higher. The water rushing over the coil seems to drive it crazy.
As for the other knobs:
I never use pinpoint. Ever, and if you learn the pinpoint trick, you wont either. When you hit a target, wave the coil over it and move the coil away from you, or closer to you. Try to center on the spot that is the loudest as you do this, and when the sound disappears, move it back until you first here it. Once that happens, the target will be directly under the edge of the coil.
Threshold should be loud enough to sound like a mosquito in your ear.
Volume all the way up
Sense - see above
Discriminate: I keep this at the lowest setting. I have had some nice finds from very low tones. 2 pieces of gold come to mind - they sounded like can slaw, very very low sounds. As you learn the machine, you will learn the different tones.
Hope this helps. I am sure the folks that have used it more will harass me for using AUTO sens, but all my gold came from auto. Cant seem to find any with the knob moved away.

Anthony