If you've come out of an office-based career, then there are a few things you can do to prepare yourself to take those opportunities when they arrive. For one thing, you should have an up to date resume and it needs to live somewhere other than your computer.
Many of these jobs are available online, so set up some online profiles at Elance or other jobs boards that target your preferred career.
Make sure to highlight your skills and competencies near the top - there'll be plenty of time for prospective clients to find out more about your background later.
Many work from home careers require you to be comfortable interacting with people on the web, through instant messaging, video conferencing, online chat and, of course, email. This is because you could be working for someone on the other side of the country - or across the globe. When you're looking to land a legitimate work from home job, your resume is just one of the tools you need. Many of the jobs sites allow you to take tests that prove your skills, too and these can help you to attract clients when you're new to the game.
It's also important to bid appropriately. The best bids give the client the information they need at the start. This includes the price you are asking for the job and how soon you can deliver. Follow this up with information that specifically responds to the points in the potential client's brief - they are there for a reason, and ignoring them could lose you the job, even if you are qualified.
Once you have landed that first job, communication and on-time delivery will secure you an excellent client rating, which will make it much easier to get the gig. Many people have started this way and ended up with successful work from home careers as freelance graphic designers, freelance writers, technical writers, freelance editors and freelance proofreaders. You can too!