An old maxim, but a true one, is that your resume should never be too long. How long is too long? Well, the ideal length of your resume is one page. This is what you should strive for, but if you are an experienced professional, with extensive work history, then that you may extend your resume up to two pages in length. If you still wish to showcase more, the appropriate place to do that is in a portfolio. For the resume, stick to one or two pages.
Remember, the purpose of the resume is to get you the job interview. There are also certain things that are expected a resume. For example, work history, education, skills, etc. You'll need to include this information, but the way in which you present it is up to you. This is called your resume's format, and it can either be chronological, functional, or a hybrid of the two.
But why would you choose one format over another?
The answer is simple, whichever one present you in the best possible light for the specific job you are submitting it for.
For example, if there are gaps in your employment history, you may choose a functional resume which highlights your skills over your experience. Or, maybe you have a very strong work history; in this case you would want to use the classic chronological format. Or maybe your education is your strong suit; in that case you would place your education but for everything else in your resume (with the exception of your objective statement).
As if that weren't enough to consider when you write a resume, you also have to think about how you will be submitting your resume. If you're submitting it online, make sure it you use all of the industry buzzwords, or key words, in your resume. Why? So that the search queries employers submit will find it your resume.
Finally, use action verbs in your resume. Never take a passive voice in your resume writing. Instead, make sure you use an active voice. This presents you in a much more positive light, and is a tactic used by sales copywriters worldwide to persuade people to buy.
Just be sure to thoroughly examine your resume for errors before submitting it for a job. Even better, ask a friend to check it over for you -- we all know one of those spelling and grammar nerds. Remember, there's no faster way for your resume to go into the trash bin than to have typos and grammatical errors.