One of the things I find most difficult about studying medicine is the very basics, and it's a topic that I find ill-covered in any of the material that I've studied so far.
Often the text with refer to, for example, O2 stats of a test-case patient. However, the text does not define the normal range of oxygen saturation for a patient, what instrument one would use to measure it, what the results of a decreased O2 saturation would be, and what the clinical indications of decreased O2 saturation are. This leaves me scrambling to either Wikipedia if I'm at my desk or to write it down if I'm not so that I can later look up the specific test and the results, and I feel it's inefficient.
Practically speaking, I am sure one can find a book outlining basic diagnostic tests, how to perform them, what results one should expect, and what it means if one receives a different result. However, I haven't yet found such a book.
Similarly, it seems as though medicine often results in such complications, and it is possible that I simply don't have a sufficient classroom grounding to deal with the basic terms and concepts- there is a great deal of interrelation between psychiatry, examination of a patient, anatomy, basic texts, radiology, and so on.
That said, so far, I have found Clinical Psychiatry (the medical text and field I am studying at the moment) exceptionally helpful. Despite being dense in format, the text is clear and readable, and presents a variety of helpful tables- such as what drugs are indicators for specific psychiatric conditions, and in contrast, what drugs one might use to treat psychiatric conditions.
It has covered the Mini-Mental State Exam in detail (a very basic cognition test) as well as outlining the clinical bases and utilities of a variety of other tests, and beginning to outline treatment regimes, as well as covering the bases of psychiatric illness.
Perhaps oddly, it has done more to make psychiatry 'available' to me than perhaps anything else has.