Keith,
First, let me welcome you aboard! Here's my 2 cents:
Start out slowly. Practice with your machine in places like your own yard, or at parks and schools in woodchip type playgrounds until you get a basic understanding of the machine, and for digging holes.
Learn the basics of your ACE150 by reading the manual. Ok, I know the ACE manual isn't all that great, but read it anyway. Read it over and over again, until you can recite it by heart. You'll be making cool finds before you can recite it.
Start off by running it in All Metal, Relic, or Jewelry mode, and get used to the different sounds the ACE makes, and how they correlate with the type of metal found. I make it into a guessing game. Before you begin digging, try to guess what the target is by the type of belltone it makes. After a few weeks, you'll find yourself getting more accurate, and you'll learn which targets you want to dig, and which ones you probably don't (although it pays to dig them all anyway!) Once you become familiar with the different sounds, you can then decide when to use more discrimination in high trash areas.
TRY to remember that the target ID feature is an accessory. It's great for IDing coins at shallow depth, but once you get to 5" or 6" and deeper targets, it looses it's effectivness quickly. So don't be dissapointed when the target ID reads $1.00 at 6", and you dig 10" and come up with a beer can or a pipe!
Make sure you have a good, comfortable set of headphones. I prefer the large, dual volume adjustable type. These are a must!!
Last, but not least, read up on local regulations regarding the hobby, and learn where you can and cannot hunt. Always fill your holes, and haul out any and all trash you find (and it'll be a lot, trust me!) And make sure you're friends and family understand that once you are hooked on this hobby, there is no turning back!!
Hope that helps some!