This is how I learn grammar: I played a lotta games that have english conversations (ex: Final Fantasy) and then i read those sentences aloud many times (sounds lame heh -.- but it does help, sir). By that way i'll remember those sentences, with the grammar notes (and vocabularies of course :>).. Besides, anime and manga help too. Since it's still schooltime now and you have to study a lotta other subjects, I suggest that you learn by heart (học vẹt) everything you're taught, then at weekends or whenever you're free, find some manga or anime to read/watch, with a paper and a dictionary nearby. When you see a new word or sentence that you find similar with what you want to study, write it down the paper, and use the dictionary to find more about it. Then review it until you know it whenever it or something similar is encountered. Just call me if needed. I'm kinda free these days hehe.
Hmm. I don't learn english through books very much. I learn it through things that we encounter everyday, like video, games, music,.... I learnt a lot from them. But well, I do have a book, written in English, which my brother gave me 2 years ago. It includes all the grammar notes in English and can help you become really good if you work with it diligently. However I've never finished it :)) Well back to the topic, you know, I started learning english when i was in 2nd Grade (9 years ago, I'm in 11th Grade now) o.o... It took me quite a while to get used to english, and be good at it. Tell me more about what aspect of english you want to improve (list, read, speak, grammar, etc................) it'll be easier for me to help you.