It doesn't matter if you're 20 years old or 50, there comes a day when you think: "I want to quit my job."

Some people get over feeling this way when their job situation improves. Others, however, never shake it. In fact, it becomes stronger every day — quitting is all they can think about.

You may be one of those people asking yourself: "Can I just quit? Can I afford it? Will I get another job? Will I only end up hating it just as much at the one I'm quitting? What will my family or friends think of me if I quit?"

While these are obviously tough questions, the stress caused by staying with a job you desperately want to leave can be worse. Research has shown that everything from depression to heart problems can be caused by workplace stress. You may finally reach the conclusion that for the sake of your health and peace of mind, you need to move on.

Still, there are some things to consider before you just walk out the door. First, you've got to decide what you want to do next. Don't focus only on quitting — focus on what comes after you quit.

"You really need to know what kind of job you want, not just what you want to leave," says Richard Lamond, senior vice president and chief human resources officer with Spherion Corp., a staffing and recruiting company.

Specifically, you should consider what you like and don't like about your current job. It makes no sense to quit one job, only to jump right back into the same situation at another company. What excites you? What bores you to tears? Are there skills you wish you had? Do you see yourself doing the same type of work, only at a smaller — or larger —company?

Give yourself a chance to dream — come up with something you would love to do. Then, more realistically, decide what parts of it are within your reach. What do you need to do to attain the job you desire?

"These days, people have to be mindful of their career ambitions and goals," Lamond says. "It's OK to think about your next job. It's OK to manage your own career."

Those who want to leave a job also should consider the current job market before making the leap. By checking out companies hiring in the area, either through online sources or through local job ads, a person can weigh the chances of landing a new position quickly.

Keep in mind that some professionals look for more than half a year before landing a new job, or must consider relocation to get the position they want.

Lamond says that once you get a new job, don't give in to temptation and start badmouthing your old job and bosses.

"It's a good rule of thumb not to burn your bridges. That means you give your two weeks' notice, and act professionally during your exit interview," he says.

And, there's another good reason not to tick off a former employer: "It may not be as bad as you think it is and you may want to return one day," he says.