Effective strategies for retaining and reusing knowledge from books

If you read any non-fiction recently, what methods did you use to retain the knowledge you gained from the book? Taking notes, making a summary...?

How do you apply what you have learned in daily life? And how will you remember doing it six months or a year from now? - Re-reading the book? - Browse your notes/summary?

I often have trouble retaining the knowledge I gain from reading books and am interested how other HN members do this.