all i can say is that the population never increases fast enough when you need them. trying to strip mining for some planet u just whacked or u. riches
And they are always too much when u dont need them e.g. 1-2 land gas or u.spazials solely for digging.
to increase population just follow what tiffany said as it is a brief guideline of how the game remains it`s logic
people live in houses, eat food and breed (but it takes time)
give them homes (housing), take care that food never runs out and give them time to be indecent (use turns)