One of the biggest mistakes job hunters make is to throw all of their experience into a resume without any regard to its relevance to the job at hand.
If there is one thing I've learned from being married for many, many, many years, it's that you can never expect another person to know what you're thinking unless you tell them. Thoughts do not float out of your brain and then magically absorb into the gray matter of another person.
And if those closest to you can't read your mind, then you can be certain someone looking at your resume won't be able to. In fact, unlike your loved ones, he or she won't even try. That's why you have to take pains to make the purpose of your resume obvious and match it to the position you're applying for instead of using a generic resume for all job openings.
For example, if you're applying for a project management position but you don't list your PM experience until somewhere in the middle of your resume, then you can't expect a busy hiring manager to slog through a list of your help desk experience until he finds something that is relevant to the job he's offering.
You may have a deep history in IT and are responsible for almost everything IT-related in your company. However, stating first in your resume that you were in charge of reducing security risk for company data does not speak directly to project management (unless you specifically managed a roll-out of a security tool).
It's also great if, for example, you have experience training people in Microsoft Windows 7 or a Cisco curriculum, but that does not directly speak to an ability to manage project teams and stakeholders. If you think it does speak to it that in some way, then spell out why. Don't expect a harried hiring manager to connect the dots for you.
You may need to use a non-chronological format to do this, but you should begin with any migrations, site upgrades, accounting systems, or anything else that you planned and managed the process for. Then you can follow up with all the incidental education and experience you have that makes you an even better job candidate.