The tough part about putting together a resume is that it's largely a blind process. You have to fish around in the dark to assemble the right combination of facts and phrasing, without ever really knowing what's right about it and what's not.
Let's face it. You send stuff out, you hear nothing from the people who tossed it in the can. So you can't really find out why, right? Well, that's certainly true to some degree. Hiring managers aren't going out of their way to inform you of why they've decided not to consider you.
Nonetheless, it doesn't have to be entirely a blind process.
Follow these tips for figuring out what's working and not working on your resume, and make your profile highly marketable.
Look at it from the employer's standpoint
As you write your resume, look objectively at it while pretending to be the grumpiest, busiest, most jaded hiring manger in the world. Read your resume while grumbling, "Why the hell should I hire you?!!!" If you can't come up with good answers for that, consider farming the resume-writing work out to a professional. The money it costs is relatively meager, compared to the potential benefits. And you'll learn great resume writing tricks you can use for your whole career.
Change the name
When you've got your resume to the point where you feel it's the very best you can do, save a version with a completely different name and contact information. You should also change the company names, or any other information that might tip associates off that this is your resume. Yeah, sounds odd, but don't worry - it's a trick to help you get more objective feedback.
Get other opinions
Now take your renamed version and ask others what kind of impression they get from reading this "other person's" resume. And don't just ask your contact generic questions like, "Do you like it?" or "What do you think?" Instead ask more pointed, specific questions such as, "What kind of job do you picture this person doing?" or "What on this resume might prevent you from considering this person for the project manager job?"
Work with recruiters
Finally, try to work with recruiters early in the process if possible. Granted, these job search salespeople are not around to help everybody. They're typically interested only in extremely qualified candidates in very specific career fields - almost the ideal in any particular profession. But if you can manage to get in with a recruiter, they can offer extremely valuable feedback on your resume. They have, after all, seen mountains of resumes. They have a pretty good idea of what will fly and what will crash with hiring managers. Temper this with information from these other methods and your resume will be vastly stronger than it would be from the typical "shot in the dark" methods.