There is much talk about tests. Justinian Lane has done a great job of pointing out how what some call "defensive medicine", actually makes doctors a lot of money. What a deal, crying about how you are forced to do something that seems to fill your pockets. Whatever it is, each person should know what tests are the best to stay healthy.
Medline, has suggested that everyone review the following:
- Breast cancer and cervical cancer in women
- Colorectal cancer
- Diabetes
- High blood pressure
- High cholesterol
- Osteoporosis
- Prostate cancer in men
Also as far as understanding tests:

(National Cancer Institute)
- Laboratory Tests(Food and Drug Administration)
- Understanding Your Tests(American Association for Clinical Chemistry)
Each test will be important based upon age, sex, and individual life factors. The key point is, the correct test at the right time can make sure that you stay healthy.