Productive Idea flow is when ideas keep on building over each other. You arrive at a good idea which is improvement over your current product and spend some time visualising how everything will look and work if that idea is implemented. Then in that state you imagine yourself there and try to find another improvement. This improvement is your next idea built over previous increment. This incremental ideas work over each other to create a new innovative disruptive idea.
e.g. In your thoughts imagine creating a light bulb, then LED, television, computer, mobile etc etc all just by a bulb.