I think the key thing to remember is that an employer honestly spends like 10-30 seconds scanning the whole thing over. And they only read more if it's evident in those couple seconds that you've got what they're looking for. So the goal is -- clear, concise, to the point. List skills and whatever relevant work experience you have. The goal is to make it extremely easy for them to read super-quick.
The job interview itself is where you can elaborate on stuff.
Length is one of those things up for debate. If this is a situation where you're handing out paper resumes, then I'm a supporter of the old school 1 page resume. Because they scan those even quicker, and some won't even bother checking the back, and some get annoyed if it's more than one page. Especially since you're in school and don't have the work history to genuinely warrant multiple pages.
Online resumes -- especially ones where you just fill out text boxes -- are different. You can put more in those. The one I just did allowed you to write up to 1000 words for your skills, and another 1000 words for each job you've held in the past. So, yeah. You can elaborate a bit. But still, you should always be concise and to the point.
.....Of course, take my words with a grain of salt, because psshhhh my work history is atrocious.
edit: wow there were a lot of replies while i typed mine out, okay then