I figured out this tip. I am not sure if new players will find it here(I would not), so if you guys agree that it is sane - maybe there is some better place to place it?
So here we go:
I find it helpful not to design any colony ships. This way shipping lines are forced to use luxury liners, which takes much less people in a single run, but generate greater profit. It might also be helpful to obsolete freighter design when you feel that you had enough of civilian freighters for now. This will force shipping lines to build more luxury liners.
Why?
Because this way you:
1. get more income.
2. do not need to produce any infrastructure beyond initial ammount, as colonies grow slowly enough to be supported by civilian infrastructure.
3. have plenty of time to plan and deploy necessary defence forces.