I have read many books on IFR and the ones mentioned here are all great. Especially Machado’s.
However, these are like drinking from a firehose for the prospecitve IFR pilot.
I found the best first book on your IFR educational journey is the simple “Instrumetn Flight Training Manual” by the late Peter Dogan, founder of the 10 Day PIC IFR training.
I like this book alot because it is a logical, easy to read brief tour through the what at first seems abstract world of instrument flying. It does not get into the minutae of procedures and chart details, nor is there tips from the old pro’s but it is succesful in getting you to understand the whole system in general terms… and THEN you go on to more detailed texts.
The second book I would suggest you read after the first is the classic “Instrument Flying” by Richard Taylor.
It has a nice style of writing and it introduces more of the finer details of the instrument flying world… after you have firmly understood the basics in Dogan’s book.
Machado’s book is still like drinking from a firehose even today. But it IS satisfying. Like others said, it is a permanenet bedside staple. it has so many little subsections, stories and tips that it makes for a great bathroom reader also! Seriously.