Since this is a request should it be in subjunctive....which would change the verb to the subjunctive....like tenga buen dia....where "tenga" is the subjunctive for tener....so likewise with "leer" in please read more books.
I used "Favor de leer más libros" which I see on signs all the time. Well, not about books, but things like "Favor de esperar aquí" or "Favor de no tirar basura". There's no context in the phrase. A library could easily have a sign that says "Favor de leer más libros"