There was a time when employers expected loyalty. In return you had a job for life – or at least a sizable chunk of it, with steady progress through the ranks and pay increases.

The social contract broke down. Employers no longer expect you to stay for ever. If they want to keep your skills, talent and enthusiasm they offer equity, options or another incentive.

When you move jobs, think about overall shape of your curriculum vitae or résumé and not just money. Balance the variety of skills and breadth of experience against the need to show stability.

It may not worry your next employer if you have only been in your current job for 10 months; future employers may view things differently.

It’s important not to look like a butterfly flitting from one job to another. On the other hand, smart recruiters know five years at a single employer might not mean five years of experience; just one year of experience repeated five times. It might also show an unambitious nature or even a lack of gumption.

There are no hard and fast rules. The details differ from discipline to discipline and from region to region. After talking to recruiters and people who successfully manage their careers, I've found:

• It’s OK to have a new job roughly every year up until around your 30^th birthday.
  If you graduate at 22, you can safely fit in seven employers before hitting your 30s. Less than three employers in this time means you won’t learn enough. Higher degrees, periods of self-employment and overseas bar-keeping each count as a single employer.
• Slow down when you hit 30.
  Each job should last between 18 months and three years with an average of over two years.
  Aim for four CV items between your 30^th and 40^th birthdays. Don’t worry if one job lasts less than 18 months— make sure you have a good explanation if there is more than one short-term job. Higher degrees and periods of self-employment are still cool. Indulgent goofing-off (i.e. overseas bar-keeping) looks flaky, but accomplishments (writing a book, sailing single-handedly around the world or climbing Everest) are OK.
• Above 40 it’s OK to stay longer with employers, but not too long and not if you stay in the same role. The lower limit of 18 months still applies but you should clock up some extended periods of more than four or five years with a single employer.

Here are the knowledge worker posts on this week's reading list:

The E-Learning Curve Blog: Emergence of Knowledge Workers: a Short History.

At first sight Michael Hanley's history looks to be too short to say anything useful. In fact, it's one of a series of related posts defining the nature of knowledge work and knowledge workers. You may like to read this and compare it with my Just who are the Knowledge Workers?

Cube Rules: Career Management Needs Adaptive Change.

Scot Herrick blogs about the difference between technical and adaptive change.

LG & Associates Search / Talent Strategy: "Making Talent a Strategic Priority": Thoughts From the Fringe (Part 1).

Ex-marine sergeant Josh le Tourneau quotes from a McKinsey Quarterly article Making Talent A Strategic Priority. Interestingly he argues the companies who make the most noise about the importance of talent are  the ones who underpay the human resource executives expected to manage the companies' talent pool.

The Cutter Blog: The New Knowledge Workers: Are they a new breed? Are they different? (Does it matter?).

Three questions in one headline here. While all are relevant to knowledge workers, you won't find the answers in this post. In fact, the post leads to a questionnaire. Author Robert Mason promises further discussion in future posts. Although the Cutter Consortium has a clear IT industry orientation, this promises to be a rich line of investigation into the way knowledge workers are (or are not) changing.

Web Worker Daily: What makes web working more difficult?

Celine Roque looks at why American knowledge workers and their employers aren't making more use of telecommuting. The obstacles apply just as much in New Zealand and Australia.

Don’t assume you can walk into a plum job just because there’s a skills shortage and you know a thing or two about your area of expertise.

Even if you look good on paper, have the right technical skills, relevant experience and glowing references, a potential employer will still want to interview you face to face – if only to make sure they are not making a ghastly mistake.

Being interviewed is an important skill for any knowledge worker to master. Once you’ve reached the interview stage you’re in with a good chance of landing the job – few employers interview more than half a dozen people for any vacancy. Most short lists are no longer than two or three people. And most interviewers want you succeed, after all they need to fill a position and they have other things they want to get on with.

The important thing at this stage is not to blow the opportunity by making a fundamental mistake. Good interviewing technique might not count for more than your skills and experience, but bad interviewing technique can  lose you work that by rights you should have.

There are five ways you can blow an interview:

1. Not preparing

As the cliché goes: you prepare to succeed, you don’t prepare to fail. It’s important to know yourself, know what you have in the way of skills, experience, attitudes, past performance, values to offer the company. It’s also important to know about the company, about its products or services and to find out who customers are, then think about where you can play a part. Of course with the Internet there’s not much excuse for missing out on this kind of basic pre-interview preparation. If possible, it’s also a good idea to check out what the company wants from its employees. You might try searching back copies of newspapers, magazines and other media to look for relevant stories about the company and its technology. Also check out blogs written by people working for the company and for what outsiders have to say about it.

2. Acting like you already know everything.

Preparing before heading off for an interview is a good idea, but don’t overdo the knowledge act. Everyone dislikes a person who behaves like they know everything. In knowledge-based industries no one person can know everything.

It is more important to show the ability to ask the questions so you can identify the issue or solution or steps to the solution. Knowing where to get the answers is at least as important as having the answers to hand.

3. Failing to tell the truth, the whole truth and nothing but the truth.

Experienced interviewers can quickly recognize which potential employees are full of hot air and which are the real McCoy. One of the biggest mistakes is lying or over-selling your skills and ability. Try this and you could quickly come undone and ruin your reputation right across the industry – it's best to assume employers talk to each other.On the whole outright lies are less commonplace than exaggeration or missing information. Whatever the temptation, it’s important to avoid all types of untruth. Should things go wrong and you find yourself in a dispute things could get nasty – there have been cases employees being sued for misrepresentation.

4. Lacking sufficient interest.

OK, so some jobs do seem dull, but if you fail to show any interest in the work on offer or the company doing the offering how can you expect them to show any interest in you? You may have to take on less exciting roles to reach the better one.The biggest mistake a knowledge worker can make in an interview is to come across as being too aloof, uninterested or not bothering to ask questions.

5. Betraying previous employers

The last thing any prospective employer wants to hear is tales about the awfulness of your previous workplaces, or worse, negative stories about people. This sets off alarm bells for every potential employer. The smarter ones suspect that it might only be a matter of time before you badmouth them.By the same token, you shouldn’t normally consider giving away insider knowledge or trade secrets of your previous employer. It doesn’t matter how justified you may feel, it doesn’t matter if your new employer is a direct competitor, never volunteer this kind of information as doing so will see you labelled as a potential traitor.