If you love reading and have excellent grammatical and critical thinking skills, it has probably occurred to you that editing could be a great career choice. The editing field is fairly competitive, but with the appropriate background and skills, there is no reason why you can't become an editor.
If you're still in school (or considering going to school), study an English discipline. Suitable degrees could include creative writing, English literature and journalism.
Write. Even if you don't want to publish your own work, only doing plenty of writing yourself can really give you insight into what it takes to craft a great manuscript. Once you've got all that writing done, you might as well to try to publish it. This can give you first-hand experience with the publishing industry from a writer's perspective, as well as showing some relevant experience if your editing portfolio is slim.
Do some volunteer editing to build your portfolio. Start with a project such as a school newspaper, a newsletter for a group you support or proofreading of friends' school papers. Save some samples of the editing you have done, especially anything that is published (if your editing includes personal documents, make sure you have the authors' permission).
Consider building more experience with freelance editing projects. This is a good place to start to become a professional editor, because many of these positions are entry-level if you have the right credentials. Search online for editing services or publishing houses that hire freelancers, or look for individual projects through a freelance job Web site.
Apply for ongoing editing jobs with a full cover letter, resume, published clips and professional references.
Since editing work is so popular, skill is important, but so is perseverance. Once you start applying for freelance or in-house positions, remember that you may have to send out a large pile of applications if you really want to become an editor.