These Oxford Chemistry Primers entered the market just over 15 years ago. Great value for an authoritative brief introduction to topics which you don't want to spend the time or money buying massive textbooks for!
I am a postdoc moving to a new area of research. I find that this book contains a good summary of what I have to know about NMR. Moreover, due to it's size you can keep it all the time close to you in case of any doubt. However, I recommend complementing your studies with a more detailed book such as Basic One- and Two-Dimensional NMR Spectroscopy