The skills section of your resume should be an accurate reflection of all you can do, but this doesn't mean that you should include every technology you've ever read a book about. You don't want to overwhelm your reader at first glance, perhaps making him look at his watch and wonder if he has time to read all you've written.
What to Include
The skills section of your resume should include details of technologies that you at least have a working knowledge of. It should also include any notable soft skills you have, such as presenting to large groups or writing technical information for a non-technical audience. The skills listed in this section should be verifiable. If you say you have experience presenting to senior management, someone should be able to verify that with a reference check.
How to Organize the Section
The skills section of a resume can be organized in numerous ways. The more neat and orderly it appears at first glance, the better. For example, a skills section that lists technologies broken into groups is much easier to read—and therefore more likely to be read!—than one that simply offers a long single list mentioning all the technologies one by one. You might want to consider organizing everything in categories such as development tools and languages, protocols, databases, platforms, and so forth.
Here are a few examples of different, well-formatted resume skills sections, categorized by industry:
Software engineer skills section: At this level, a resume might simply list three software skills in bullet points—databases, software, and languages, with a brief inclusion of the various platforms and programs for each. Bullet points tend to be less intimidating at first glance than long paragraphs. By their very nature, they lend themselves to easy review and digestion.
Senior software engineer skills summary: If you're going for a senior position, you might want to flesh it out a little more, "little" being the keyword. Remember, brevity is key. Consider writing your resume on one day, then going back to it the next day to read it with a cold eye. See if anything jumps out at you as being extraneous or repetitive. Keep in mind that if you have prior experience in a senior position, it goes without saying that your skills include the most basic abilities in the field. Focus on the unique aspects of the trade you've mastered.
Skills summary for mechanical design engineer: A resume for this position doesn't really need to include a "skills section" at all. The really pertinent information to the position being sought is encapsulated in the education and accomplishments sections. Again, the reader can accurately presume that with advanced education, you have the necessary basic skills to do the job. Additionally, including the list of accomplishments indicates that the applicant knows how to use these skills. Redundancy won't enthuse your reader and it's a waste of your time as well.
The bottom line? Review your entire resume, not just the skills section, to ensure that you're not repeating yourself, belaboring the obvious, and losing your reader.