In first approach you find short articles or blog posts about desired subject, read it and then try to find all other parts that you need to learn. In this way there is an opportunity to consume your time in an efficient way by not reading none interesting parts of subject. And there is a threat that says you won’t create a complete picture about the subject in your mind. For example some times you will never realize if ever exists a special feature in a technology or just it is you that don’t know anything about it.
In second approach you consume more time for reading (and practicing) whole book or manual. But instead you will understand anything about it. And you will enjoy of a complete reading. Notice that in this approach you still have the chance to by pass unrelated parts.
Recently I was forced to learn SVN, a well known source code management software. As described before I preferred to use second approach by complete reading svn book. This book covers all needed commands and have been partitioned into some chapters very nicely.