Mainly the ability to "tell" if it's a gold ring versus say a tab is based on audio response. If you get real good at hearing what the machine is saying then that will improve your odds at identifying gold. Luckily the GT's outstanding audio details provide the best subtle telling traits between gold and tabs or other junk than any machine I've owned. Even if they both have the same ID the gold ring often will sound smoother, warmer, round, softer, etc, where as trash can sound harsh, tinny, bouncy, bangy, rough, washed out, etc.
Not all machines have this ability to provide these small differences in audio. Some are better than others. The MXT or M6 for instance are very good at this, though not as good (not as many tones and other things, not to mention not getting nearly the depth of a Sovereign) as the Sovereign. The main thing is to use a machine that has very telling audio and then to learn what it is saying. A friend of a friend uses an MXT and he has learned it's language on rings very well from what I hear. He always seems to be finding gold rings on land, as that's his primary target when he hunts.