until i went to grad school, i would go to the library and just grab a book that had a title and entry pages that grabbed my attention. now, after a few classes, i am realizing that it's all about the author. is the author reliable (as a source) or is the type of author you read for pleasure? once that is determined, then you can sit down and read your book for the purpose you want.
i just read a good article about alexander thayer. he spent 17 years on his first volume of the 'life of beethoven.' then 32 on the 2nd-3rd. they weren't even completed in his lifetime (that shows you how precise he really wanted to be). he interviewed people in beethoven's day (ie anselm huttenbrenner, in whose arms he died; caroline van beethoven, widow of nephew karl, charles neate and cipriani potter, the english musicians that had been his pupils, sir george smart, who had visited him to learn the proper interpretation of the ninth symphony; moscheles, who had been his professional associate in vienna; otto jahn, who had undertaken a task like thayers, but abandoned it and turned over his gathered material to him; mahler, an artist, who had painted the composer's portrait; gerhard von breuning, son of beethoven's most intimate friend, and cheery bedside companion when beethoven was dying. this is most helpful, to get closest to the source of the material.