The best way to fit more population into the same amount of space is to destroy older, outdated settlements after you upgrade your housing. To do this, you’ll need God Powers, which are unlocked after a certain population level, and accessible by tapping on the belief counter. Use the Finger of God to destroy an old settlement, and have your people build a new, up-to-date one on the same plot.
A fast way to get belief from rocks is to do the following. First, hold your finger on a rock in order to destroy it. Then instead of releasing your finger, start dragging it around the screen and finding more rocks. Slide your finger over any rock to destroy it and gain belief. The same thing works for trees, but you have to tap a tree first in order to make it work.
Once you have the God Powers, you will be able to create a settlement, which allows you to build farms and mines in order to get wheat or ore. You can string multiple abodes together to create a settlement. So in order to be able to create as many settlements as possible, make sure that your land is as flat as possible and then load it up with plots and abodes, so that you can either convert them into multiple settlements or one gigantic settlement.
Treat your ore and your wheat just like population – you will have a set amount of ore for each mine and a set amount of wheat for each farm that you build. You’ll end up needing more ore and more wheat to build abodes and settlements, and inevitably, at some point you’ll end up stuck, which means you’ll need to increase your population. Aside from the tips above, build monuments that affect all nearby abodes in order to increase your population again and enable more farmers and miners (and builders, etc etc).
If the going really gets rough, figure out which landscape gives you the best abodes, and take advantage. Build up a ton of belief to do this. Start converting your (for example, if grasslands give you the best houses) beach areas to grasslands by knocking off the abodes and dragging new layers over old plots. Then expand the green layers all over your beaches.
Keep belief in handy too so that when other tribes start to harass you, you can build new layers on top of them and bury them, which will make them go away if you bury them with two or more layers. That, or start deleting layers out from under them until they fall into the water and drown.