Definately keep it at around 50% on the sensitivity. I have had the best success in the jewelery and coin modes, the all metal picks up, well, just about everything. Pinpointing is right on the money so far. Hold in the button and slowly move it across the signal. I find using the "X" pattern works well, it enables you to really focus in on the spot. When all the bars are lit up across the display and stay there while not moving the coil you should find your target right on the inside of the top of the inner coil. If you are in soft ground give it a little push to make a pattern and you'll have a good place to start. The learning curve on this machine is pretty friendly, the more you get out there with it the easier it will come.
Oh, your id feature should give you a very close indication of what is down there. In the above mentioned modes I have found that .25, .10, .05 and pulltabs are true to the display. Pennies are sometimes a bit vague, but the others give a nice solid beep-beep-beep. In all metal aluminum and iron will give a much lower tone with a hit to the far left of the display.
HH