The key to effective character presentation is contrast.
Think about it. If your heroine is just like a typical heroine in your genre, she’ll be boring and two-dimensional. If she’s just like a minor character in your story, she’ll again be boring and two-dimensional.
Contrast your characters both against other books, and against other characters in your book.
The first is harder, but I keep in mind Donald Maass’s advice to make your characters larger than life. Make them do things you wouldn’t do. Make them better than who you are, make them even better than your real-life heroes.
I’m not saying to make them perfect, but to make them richer. The most memorable characters in fiction are those who are out of the common mold, with multiple facets and a dominant impression on the reader.
Also make sure your characters aren’t too much like the other characters in the story. The most obvious method is to make sure their dialogue differs.
I’m not saying to give them different accents or dialects, but vary their sentence structure and vocabulary. Make it obvious to a reader who is speaking even without speaker attributes.
Contrast your characters, and make them jump right out of the page.