Grammar Schools expect their pupils to be independent in student's learning and organisation. You are expected to know a lot of the basics before you enter a lesson so you should spend your time going over the textbooks. In terms of the students, they are quite competitive with each other (ie they are always comparing grades and sport achievements). The grammar school that i am currently attending has a major focus on extra-curricular activities such as chess, debating, STEM challenges, national competitions so there are lots of clubs and societies you can join. So, if you want to join a grammar school you should be prepared to an active learner, a social person and a confident person.