Is my advice to girls on social media, that they should not post eye-catching pictures of women and men and that they should choose beneficial novels for their reading lists, correct or incorrect?

Advising girls is not wrong; rather, it is correct, and you will receive a great reward for it if your intention is good, while paying attention to the content of the stories and the ruling on reading them based on whether they contain Sharia violations or are free of them, and the importance of preserving time and not spending it except on what contains religious or worldly benefit.