What you’ll focus on will depend on your purpose for reading the book. The enotes study guides are an excellent place to start, because they will give you the big picture. Even though I teach this book, I also find the questions enlightening. Some are familiar, but some give me new perspectives.
Focus on Pip and how he grows. This book is a coming of age story, so that will be important. You also want to look at how social class is portrayed, and how people move from class to class.
Finally, remember that this book is a mystery! Watch out for clues, because there are plenty. You might be surprised at the ending.