One of the most common deficiencies, and one that will really make you miserable, is Zinc. Zinc is an essential mineral that is really only stored in large amounts in the eyes, where it is needed to give us good color and night vision.
The Zinc Taste Test is for determining whether you need to take Zinc. You can also use kinesiology, of course.
This test is best done with liquid zinc, but you can also use chewable zinc lozenges, preferably ones without any flavor besides peppermint.
Zinc
Zinc is a metal and so tastes very metallic. Put a teaspoon in your mouth and swish it around for one minute, OR put the lozenge in your mouth and start chewing. Does it taste metallic right away, or does it take more than 30 seconds for you to taste the zinc? If it does, you are very low on zinc and should supplement it.
Zinc is best taken 2x a day. It takes about 3 months to really alter the cellular levels of zinc, so plan on supplementing therapeutic doses (50 mg a day 4-5x a week) for 3 months minimum, then just be sure to get the RDA.
If you are prone to anemia, be sure to take the zinc apart from your iron sources, as you can only absorb either iron or zinc. Same with calcium. You can also supplement Iron and Calcium to be sure you get your needs met.