Part of it is just leveling up your citadel. Some is the game dripfeeds new systems and buildings to you that make things more complicated but also help with happiness. A lot of it is just learning what it takes to keep people happy.

Keep playing on difficulties that feel manageable, and when it starts to feel like you can handle it, then bump up the difficulty then.

In the harder difficulties, you have to micromanage everything all the time, and it takes forever.

Some towns are just going to fail if you're unlucky... But you can set yourself up for success by learning which Services buildings to pick. Some like the Temple (reduces hostility) and the Guild House (increases resolve every time you buy/sell) can be instrumental to surviving harder difficulties.

Make sure you have housing for everyone, upgrade your hearth, and unassign your woodcutters during Storm.

Citadel upgrades for essential blueprints of race specific housing and field kitchen will help keep resolve up in the early game.

Cornerstones the reduce hostility will help a ton in the mid to late game.

Edit: And don't open a glade unless you have a reason to. Every glade you open increases the hostility level.

Personally I don't open small glades unless I have a cornerstone that triggers off it or my humans or foxes have seen something there. I'll spend the first 2 years building up my initial settlement, then start of drizzle year 3 break open a dangerous glade for those sweet event rewards. I'll continue to open a dangerous glade every year or two afterwards depending on how things are going.
Much like how once you get comfortable with the difficulty level it's time to increase it, once you feel comfortable with how your settlement is running it's time to open a dangerous glade.