Management thinking is inherently faddish, but there are some favorite themes that never fall out of favor. Innovation is one those evergreen themes: it is a rare CEO who doesn't list innovation as one her top four or five priorities.

But innovation is an elusive beast. Setting aside a few well-known exceptions, the vast majority of established firms feel there is a big gap between their efforts and their achievements. R&D investments have been made, stage/gate processes have been built, creativity training courses have been run, and yet the outputs — exciting new products and services — don't seem to be falling into place.

So what to do? We can look to companies renowned for innovation — like Apple and Google — and try to learn from them. But that's a flawed approach. Apple and Google have innovation in their DNA; they have many years of success to build on; and they have earned the license to take some risks. So we have to be very careful in applying our learning from these two to our own companies.

I think a more useful approach is start from the principles of innovation — the underlying ideas and themes that have been identified over the years — and to see if we can find ordinary companies that are putting those principles into practice. And when I say ordinary companies, I mean established players that are trying to reinvent themselves, and also mid-sized firms that are away from the spotlight, looking for new and better ways of working. If these companies are successful, then they are likely to be much more effective role models than Apple or Google are.

So what are these principles, and who is experimenting with them? Here are three that I think are really important, with a couple of company examples for each one. Find out more about Harvard Business Review's three.