Like any major life change, switching to a career you're passionate about takes some good, old-fashioned planning.
If your dream job involves working for yourself, you need a business plan and a savings plan, so your career change doesn't spell financial disaster. Consider this your exit strategy, and take the time to crunch some numbers. How much income will you need to net, after taxes, insurance and business expenses, to make ends meet, and how are you going to meet those goals? Most entrepreneurs don't turn a profit right away, so it's a good idea to save up at least a year's worth of expenses. Even if you don't end up having to tap into that nest egg, you'll be glad you have it in case an emergency comes up.
Looking to work for your dream employer? Read up on the company and familiarize yourself with the industry. Do you need additional training to get the job you want? Take some classes or look for an internship where you can learn the skills you need to get that ideal job. If there isn't a particular opening or position that you have your eye on, stalk the company's Web site for job listings. It may feel like applying through a company Web site sends your resume into a black hole, but that isn't always the case.