This is a good question. There are a few areas I would suggest you consider: 1) Typos and grammar - Be sure to proofread your CV carefully, and have a friend or mentor read through it as well. When an applicant's resume has typos, this is a very negative factor, and often the reason that we don't continue with a candidate. 2) Clarity of formatting and layout - If you're applying for jobs that require visual skills (such as graphic design, or something artistic), the overall appearance of your CV is particularly important. However, I would suggest you consider this factor no matter what the job. You want the CV to be easy to read, so that people are more likely to spend time looking at it. Think about consistency of fonts, spacing, bolding text, etc. 3) Tailor your CV to each job - You'll want to make sure that the experience you highlight is relevant to the particular employer who reads the CV. Of course, list all of your experience (especially if you haven't had very many jobs), but be sure to note specific tasks or skills that relate to the specific job you're applying for. 4) Length - I would recommend you keep it to one page, unless you have a situation where you need to list a lot of additional information and it just won't fit (such as if you had published a lot of articles and needed to cite all of them).
If you're making a resume for the first time, I'd recommend you start with brainstorming all of your experience (including volunteer or school activities) and listing it in chronological order. Then you can work on formatting and writing about your jobs with "resume language." If you have a teacher or mentor who can help you with this step, or edit your draft, that might be a good idea.
Hope this helps. Good luck!