i find that doing practice papers open book is an efficient way of learning and summarising new content + practicing exam technique simultaneously
but obv u wanna be doing as many closed book papers as possible once u learn the content
semi open book. spend slightly longer reading time then you would normally, to make sure you thoroughly understand what each question is asking, and circle the questions that you don't know how to do, or you haven't covered in class yet. For those that you don't know how to do, maybe instead of just looking at the textbook/solutions. Write out how you might approach the problem (the strategy) e.g. I would use X method.
And then consult the textbook to see what methods/tools you can use, attempt the problem and then check with solutions.