Your resume is arguable the single most important part of the application process. A well-organized, relevant resume will set you up to get an interview, while a poor resume will get completely lost in the sea of applicants. This is a fairly modern concern, as job postings now get thousands of online applications a day.
One of the biggest mistakes you can make when applying to jobs is sending the same generic resume out for each one. Sure, you can apply to more jobs if you don’t take the time to personalize your resume each time, but chances are you won’t get interviews from any of them. If you take the time to tailor your resume, even though you’ll be applying for fewer jobs, you’ll get more interviews.