Hi Cori
Diagnosing humans, computers, and cars that do not start requires the same discipline.
Look at the simple things first then move on.

I found doctors who learned their practice in 3rdWorld Countries or the country away from expensive diagnostic aids do the best diagnosing. A good book I used while in Iraq was 'Where there is no Doctor'. You can buy it online. It was written for Central American Missionaries who often worked with the local Shamans to help the population. It is written in a straightforward language and even I could understand. It was recommended to by by a Independent Duty Corpsman who worked all over the world often in the Jungle.

However most maladies like pink eye are the same everywhere.

"All I want is a weeks pay for a day's work"
Steve Martin