My first tip would be to use the Pro Zero mode.
This will beep at just about every target but iron (if you discriminate it out up to 30-35), but the tones will sound different than standard coin shooting mode.
Coin shooting mode will often give you a false signal (that sweet high tone), if you pass over a target too quickly. The machine hasn't had a chance to read it yet, so it signals high to make you go over it again.
It can still happen in Pro zero, just not as often.
If you are losing targets it could be a ground balance issue, you haven't checked your target two ways, or it's a pull tab. Those suckers for whatever reason jump around.
If you haven't got a handheld pin pointer like the Garrett Carrot, then I strongly suggest getting one. This will cut your frustration level in half when looking for those targets.
Nails in dark dirt can be a bugger, some coins in beach sand can be just as bad. Bobby pins will drive you nuts, but as I said earlier pull tabs will be a biotch.
Some carry a small magnet with them to help find that tiny target that your eyes just don't pick up.
Also practice your target locating with a known object buried in the ground.
Follow this link to how I locate targets off the tip of my detector.
http://www.treasurenet.com/forums/metal-detecting/535837-frustrated-plz-help-2.html#post5350486
Also dig a plug big enough so that you don't scratch your target, but at the same time increases your chance of getting the target in the middle of your plug.
A good target if pinpointed properly should always been in your plug, or just off to the side.
A bad target (pull tabs, some nickels, nails, bobby pins) will often fall just outside of your plug radius.
Don't shy away from pull tabs though, as often times they are the same numbers as gold.
I hope that helps.
Good luck.
