By this I mean simply that you think about your learning; that you come to understand your own strengths and weaknesses, your likes and dislikes. If you find something difficult, you ask yourself why and try to find ways to do better next time. If you always seem to get low scores in vocabulary tests, you analyse your methods of studying words. If you don't like to study grammar in grammar books, you find some other method of learning the rules of the language. An excellent way to reflect on your learning is to keep a language journal in which you write about your daily experiences in learning English.
A good way to use the study notes on this website is to first reflect on (and maybe write down) your own strategies in listening, learning vocabulary etc. Then you can read the notes in these pages and compare what you do with the advice given there. (If you don't know how to start, just look at the sub-headings within the note pages. These may give you a good idea of the different issues connected with the particular topic.)
Remember that everyone has their own learning style. So if you do something different and it works well for you, don't feel you have to follow the advice given in the notes.