There is no hard and fast rule about the length of resumes. Check the job advertisement or position description for any specific requirements that an employer has around the length or formatting of resumes. If there are no specific requirements, generally around four pages should be adequate to detail your experience. The main thing to remember is that you highlight your skills and experience and how they relate to the position you are applying for.
Where do you start? The purpose of the resume is to detail information about you and make you stand out from others. It needs to be easy for employers to read and using headings to highlight various sections of information can help with that.
Have a thorough read of the position description or information about the vacancy. In addition to selection criteria or specific questions you need to respond to, there will be information about the key responsibilities of the position. These key responsibilities or any information in a section about the role will give further insight in to the actual tasks of the job. Make a list of these and where applicable adjust your resume to highlight how your experience aligns.
List out any formal qualifications and professional development you may have undertaken and when the qualifications were gained.
When detailing your work experience, list the jobs or experience you have had in the last 10 years. Again, use this as a guideline as you may have experience that is relevant to the position that goes beyond the 10 year mark. If it is relevant to the vacancy, include that experience in your resume.
Once you have got all your information together, have another read of your resume. If you need to cut back a bit, you can look at combining roles. For example if you have worked in the government for a long period of time with the a variety of experience across a particular stream, you could list it as Various Administrative Roles with the time span eg 1999-2009, and summarise tasks and skills you gained from those roles. There is no need to include information about your hobbies or what you like to do in your spare time unless the job description specifically asks for those details.
Nearly finished? Print it out and read it out loud. Make sure you check for errors. Most people will list attention to detail as a skill and spelling or grammar errors can easily cause your resume to go in the reject pile. Lastly, get someone else to read your resume as it is easy to miss things when you are familiar with the document.