Feel free to do some more research, but in general, breakin consists of the following:

1. Don't lug the engine (lugging means driving at low RPM's in a high gear) -- more a concern for manual transmissions I think. This is bad because it causes a large strain on the engine.

2. Don't drive at a constant speed for a long time. As has been discussed, a "long time" is not clearly defined in most places. But this is the reason that they tell you not to use cruise control during the breakin period.

3. You are supposed to give it hard (not insane) acceleration up to the max RPM's suggested for the breakin period, because this seats the compression rings. I don't think this means to do this at every opportunity, but to not baby the car.

4. Stay below the RPM's levels suggested by the manual. With motorcycles, the instructions seems to be more explicit and gradual: don't go above xx rpm's for the first xx kms... then don't go above .. rpm's for the next xx kms, and so on...

5. [EDIT: added] It is generally practice to do the breakin in cycles of heating and cooling. It has to do with the expansion of components (that are meshing). So -- for a race engine, they would run it hard, then let it cool down completely, then run it hard again, etc until the breakin is complete. For a regular car, driving it during the day and letting it sit at night is probably good enough to get that effect. But this is why it's not a great idea to breakin an engine by driving it 1000kms straight without stopping.

Then there are the recommended oil changes. Just follow the manual. Some people change it more frequently at the beginning, because as the new components "mesh" they create tiny metal filings. If you leave those filings in there too long, there's a greater risk of having them etch hard components, etc.

There are differing views on breakin, and you'll have to research to make up your own mind but in general, at least do what your manual says.

Hope that helps.