(FORTUNE Magazine) – Most of us still play under the old rules of jobs and careers. In examining your own attitudes, watch out for these old rules -- and replace them when you find them.

-- Don't leave a job when good jobs are so hard to get. Remember: The same thing that makes other jobs scarce makes your present job only a temporary expedient. It too is going to disappear. This is no argument to make ill- considered moves, just a challenge to the rule you are depending on. It is dangerous. -- The best jobs go to the people with the best qualifications. This rule is a half-truth because it fails to acknowledge that the whole idea of qualification is changing. The old qualifications included degrees or other formal certification, length of experience in a similar job, and recommendations. Today most recommendations are known to be hot air and tail- covering platitudes. Experience is more likely to produce a repetition of the past than the kind of new approaches that today's conditions demand. And there often isn't any degree or certification in the activity that today's organization needs. The new qualifications are that you really want to do the work (desire), that you are good at what the work requires (ability), that you fit that kind of situation (temperament), and that you have whatever other , resources the work requires (assets). Those so-called D.A.T.A. are the only qualifications that matter in a rapidly changing work world. -- Getting into the right business assures a secure future. The Dustin Hoffman character in The Graduate was told to get into plastics. Today it might be computers or biotechnology. But designating any field would be bad advice because while parts of the economy are surely destined to expand, no part of the economy is immune from de-jobbing. -- Don't try to change careers after 40. The world of jobs is full of age discrimination, but that's the world you are leaving. There is far less age discrimination in the world of You & Co. Vendors get paid what they can show they are worth. Those age-related bugaboos health insurance and pension contributions are things you are going to take care of yourself, so they aren't a factor the way they were when you were looking for a job. -- It doesn't matter what you want. It's what "they" want that counts. Most of us were raised on this one. Maturity was a matter of tempering our wants and conforming to what someone with more influence or resources (like IBM or the state department of education) wanted of us. But today it doesn't matter nearly as much as it used to what an organization wants. The power has moved elsewhere; the only "they" that matters much anymore is customers. Since what you want is an important part of your D.A.T.A. -- that is, of your qualifications -- you'd better pay attention to it. -- You have to be a salesman to get ahead today. Another half-truth. The old- style salesman who could sell anything is as much at risk as any other job holder. Far better off is the person with a clear product that she or he believes in. The truth element in the idea is that people will need the ability to conduct quid pro quo transactions involving not the old-line salesman's gift of gab but a clear understanding of why someone needs what one has and the ability to make that case effectively. Many people who do that well have no experience or interest in sales as a field. -- If you have responsibilities -- people dependent on you -- you can't leave the world of jobs. This rule misidentifies the risk. If you have responsibilities, it is more important for you to look ahead and develop the kind of career that has a life expectancy beyond the end of the year. Risky and responsible have been redefined: The good job, once the definition of responsibility, is now a very risky business, and the old kind of freelance activity that was once risky is now in tune with the future and is becoming the choice of many people who want to act responsibly.