Far too often, especially online, I meet wannabe writers who claim they don't read as much as they write as though this declaration means they are more earnestly dedicated to the craft than the rest of us. Reading may be as important to writing as writing itself; no amount of education, of any kind, will teach you more than reading - except maybe learning to read critically.
If you really enjoy a piece and know how to read critically, a second read is always important. Your enjoyment the first time through comes from being caught-up in the story. You are unlikely to notice things like structure, pacing, even plot and character development because you are so enrapt in the story that these things go unnoticed. If they are done poorly, they stand-out like sore thumbs - they take you out of the story and you can't not notice them. The second time through, you already know the story so you can keep an eye on how the author works to achieve that suspension of disbelief and carry the reader along.
If you prefer, take notes while you read. Books with wide margins provide plenty of room though your notes can prove hard to find later. Notepad or a similar program can prove most useful here. Include the page, paragraph, and even sentence number along with your notes. You might also purchase a Cliff's Notes of the book and keep your notes in there. It can also provide great insight on everything from symbolism to language use and more - things you might have missed on your own.
Even without taking notes, you should read widely and voraciously, even in genres you don't care to write. Everything you learn is applicable to your development as a proficient, efficient writer.