I haven't played this in about a week or two.
Some context... I had massive residential zones laid out. I had a problem with empty green spaces and general population growth. My RCI was low, and my population had balanced out.
I started experimenting with taxes. I initially tried decreasing residential taxes to try spur population growth. I went with the logic of lower taxes would encourage growth, as high taxes in the game can cause an exodus.
I lost a fair amount of money, with no growth to show for it.
I put my taxes back to 11% for residential.
I then began to experiment with policies. Particularly tax relief for residential. Since this was mostly low-density residential, I put tax relief in for that zone.
I increased taxes to 12%, which is about the peak before you begin to have problems. With the relief, this became an effective tax of 10%.
This caused my population to explode. I went from a stable, fluctuating within reason, population to a large spike in growth. +400, +500, +600 even.
I basically doubled my population, which means more tax revenue, which would offset the loss from 11% before to an effective rate of 10% after.
I've found treating the playable area as a county (instead of a massive city) with zones/districts as cities works better to keep the pop growing. I almost never mess with the taxes.
Increasing the land value usually solves stagnant population growth.