Content and length
Resumes should be two or three pages, printed on one side. This limits the amount you can write. If you feel the information you are writing is relevant to the employer it is a good indication that you want to include it.
Firstly, identifying what is relevant to the employer
Before you write your resume, consider the requirements of the employer. By looking at the job advertisement and selection criteria in the job description (which you can request from the employer) you will know which skills, experiences and qualities are important in the role.
Secondly, identify how you meet the employer's requirements
All your experience from university, voluntary work, your home life, work experience can be used in your CV to show that you meet the employer's requirements.
Information to leave out
You should not include information that an employer might use to discriminate against you such as; age, marital status and health. Only include these if they are directly relevant to the job. You should also exclude salary information/preferences.
In summary - your resume needs to be concise and relevant to the employer.