This is by far the biggest mistake of all resumes, technical and otherwise. Your experiences are worthy for review by hiring managers. Treat your resume as an advertisement for you. If you've got a valuable asset that doesn't seem to fit into any existing components of your resume, list it anyway as its own resume segment. As a rule of thumb, resumes reflecting FIVE years or less experience should fit on one page.
More extensive experience can justify usage of a second page.
Avoid lengthy descriptions of whole projects of which you were only a part. Consolidate action verbs where one task or responsibility encompasses other tasks and duties. Omit needless items. Have a trusted friend review your resume. Be sure to pick someone who is attentive to details, can effectively critique your writing, and will give an honest and objective opinion.