The graduate school application process has lots of components and how you assemble them will determine how well your application is received at each school. In many areas you have significant influence over the quality of the credential and in nearly all cases you influence how the credential is positioned within the application portfolio.
If you consider the school you are applying to and study it a little bit before assembling an application, you can materially improve the quality of your application. Tailoring your credentials to show a cohesive story of what got you to the point where you are considering a master’s degree and where you see your career going, is the best way to ensure your application package is as good as you can make it. Of course this isn’t always easy.
Treat the graduate application process like the first graduate level research project you have and give it serious focus. After all, the successful outcome is an admission offer to each of the schools you want to attend. Slacking on the application process means you forfeit options later because you were not admitted to as many schools as you possibly would have been.
Stepping outside of your own perspective may help you treat your application more like a research project and make it easier to objectively see your strengths and weaknesses. If you have trouble seeing what a school values or how your own portfolio matches up, get help. Ask someone else to look at the schools you are considering and give you their candid assessment of where you are strong and where you are weak. If you need it, get professional help. It isn’t for everyone, but there are professionals that have a deep understanding of the admissions process that can help you.
I don’t think any application guidebook can address all the possible questions or issues that an applicant sees during the admissions process and encourage you to engage the program director or admissions office directly. In fact, these professionals should be your very first point of contact and greatest research resource.