"Remember that you are going to dig trash, especially at first. I am willing to bet that after you find a few handfuls of clad, you will be able to tell a coin at 4" or less from trash just by tone, ID, and poinpoint. Hang in there.
When you do find coins, remember also that your ID isn't going to be one hundred percent accurate in ID'ing one coin from another. Dimes often ID as pennies and vice versa. Nickels are tough - pull tabs will fool you, so unless you want to give up on nickels (and gold), dig the pull tab ID's if it's locked on that target or if it jumps between nickel and pull tab. Quarters and above are the most accurate, although a quarter will often bounce between quarter, half dollar, and dollar coin.
In general, if your target ID is bouncing from coin to foil and back, it's probably trash. (Not always, but probably)."
The above quote is from epi-hunter in response to a post I made when I first got my Ace 250 in the middle of December 2005. I hope this helps. Also, to prevent "falsing", run your coil cable staight up the shaft (for 12" to 15") and tape it to the shaft to prevent it from flopping around and set your SENSITIVITY to 4 or 5 BARS, you will still get good depth at these settings.