Lots of good advice has been given here already. Like you, when I first started, I began to get frustrated at times. I thought about giving up the hobby more than once. I'm glad I didn't. My hunting buddy was a lot like you at first. He wandered a lot, had to dig every signal just in case it was good (usually wasn't), and almost never made any good finds. While we hunted, he watched me skip targets, pick and choose what to dig and what not to dig, and eventually got over the feeling that he had to dig every little beep. Now, he is finding about as much good stuff as I am, and I'm sure we both could do better still with more experience under our belts. I'm not new to the hobby, but only been doing it about 2 or 3 years...so I'm not a vet either. I have hunted lots of sites that "should be good", but didn't pan out. I hunted an old school--early 1900s yesterday, and didn't find one single old coin. Lots of pennies and dimes from the 60's and 70's though. Sometimes it's not in the cards.
Some folks say dig every target. In truth, that's the way you'll pick an area clean, and in very trashy areas, it may be the only way you'll ever find the older deeper stuff. My problem is that I don't have much time to detect, my area is extremely trashy, and I sure don't want to spend my time digging up garbage. So, although I'm sure I miss lots of good targets, I generally discriminate the trash, turn the sensitivity down a bit to keep the false signals down, and try to find repeatable signals. On the ace, and most other detectors I've used, a good coin signal is repeatable 75-80% or more of the time from side to side and front to back across the target. The deeper ones don't always repeat 100% of the time. The deeper ones might switch ID on you every once in a while, but the ID should stay the same for the majority of the time. Signals that jump around a lot on the ID bar are usually junk. There are exceptions, but if you spend your time digging those, you'll be hauling up junk way more often than not.
My buddy also had trouble with aluminum cans. Someone already mentioned trying to determine the size of the object before digging. A coin will usually ring up in a circle around 4" across or less if it's deeper...or a bit larger if it's on the surface. A can will ring up in a much larger area, usually 10" across or so, depending on depth and how the can is situated/crushed. If you get a dime signal that covers the ground in an area of a dinner plate, it's probably not a dime. a deep dime might only register on the detector in a 1" spot on the ground. I dug a couple mrecury dimes about 9 1/2" deep earlier this week, and the singal could only be heard in one small spot over the ground.
Pay close attention to the ID meter. When you get a target, note how it behaves. Different targets will behave differently. After some hours under your belt, you'll begin to see patterns and eventually these patterns will help you skip the junk, and pick up the good stuff.
This should get you finding some good stuff eventually, so that you don't lose interest. Then, when you get your detecting legs, you can go back to the places you hunted in this style and increase sensitivity and drop discrimination and learn to better discern good targets from bad. If you happen upon a hot spot, go ahead and dig it all. Tokens and gold jump around on the ID bar, and also targets in the ground can interfere with or mask other targets. Once you clear the more obvious targets, the deeper, less obvious targets will begin to appear.
Sorry so long-winded...but I know the frustration you feel 'cause I've been there too. This is my advice, and maybe some of it will help you find enough stuff to keep you interested. You'll get good in time.
