Firstly, developing the plot. She did such an amazing job with this because every tiny little detail came back to the big picture! Even things from previous books, such as the invisibility cloak, came back to the second book and I'm sure will have many purposes in books later on. Like the diary from the girls' bathroom that Harry found in the second book, we thought that would give us maybe on clue. But as it turns out it sums up the victorious ending of book 2, Harry Potter and the Chamber of Secrets.
Next, creating imagery. One thing I noticed repetitively in books 1 and 2 is the imagery. Not only visualizing people and the setting, but also the food and feasts! I saw a number of times where they would walk by this glorious food she describes and it feels like you're looking at it! Another place I found great imagery is when she describes The Forbidden Forest. She makes it sound mysterious and spooky and like a place you would not want to step foot in (but Harry's atleast been in it twice now).
Finally, loveable characters. There is no such thing as a good book if you don't like the characters you're reading about. Harry is this quiet but adventurous boy whose best friends are Hermione, smart and at first somewhat of a know-it-all, and Ron, a redheaded boy who has 6 other brothers and sisters. She goes into depth on all of the characters so well and it almost makes you want to be their friend.
