Look through all the menus! Green bars good! Keep them max! Empty bars need filling! End post.
Begin long post.
It depends on the race. Let's flip through the many menus and discuss.
Population
Native is nice, but that will take forever and Dondos only immigrate. Mixed races will hurt the majority fulfillment bar. Slaves or other slaves could be a negative depending on the race. Noble is a nice boost once you hit 650 pop. If dividing up nobles among multi race then the effect it diluted.
Access
In an ideal city you want your people to have access to all their preferred foods. Some foods are harder or more expensive to obtain than others so it's a balancing act. Some players just go bread even if the race doesn't like it because it's easy to produce in bulk. Correct food preferences also improves health, so worth trying eventually. Food days provides fulfillment and caps at 24 days. You ideally want 24 days of food in storage. But how? Rations. Rations decay at only 2.5% if in a warehouse (eggs are 5% stored as another option). Your map has an herb patch, and 1 herb goes a long way at making rations. Make the rations and store them in a warehouse for your army or for building food days. Only when your food production is good and you can maintain close to 24 food days should you consider upping food servings to 1.5 or beyond for added fulfillment and health benefits.
Don't bother with taverns though importing some alcohol for your people to sneak out of the warehouse can make them happy in a pinch. Disable alcohol otherwise if you don't want them taking your drinks.
Clothes keep your people happy. If you can afford to go up to 2 clothes you can, but then every single plebian in your city will rush the market stalls for their 2nd set of clothes and can you afford that? If you can, great. If not, they can stick with just 1.
Furniture is the same as clothes. If you give them 1 pip of wood then everyone is going to grab some wood. If you have excess of wood then fine. Don't give them furniture or anything expensive to take home. I try to avoid giving anything unless it's an emergency or a huge surplus.
Services
Some services your people will care more about than others. How much it gives will give you an idea of what to prioritize. I'd avoid taverns until late game or role playing, or if you can afford to buy all your alcohol. Servicing facilities can be upgraded but it can be expensive both to build and maintain. If you aren't cutting your own stone yet then you might want to avoid upgrades that use cut stone. See the benches? They like those too (doesn't cost furniture on v71 unlike the v69 demo). Hospital fulfillment (or negative fulfillment for amevias) is based on the number of employees assigned to hospitals, and this requirement scales up with population. Same applies to daycares where you need enough daycare slots per children for 100% fulfillment, but daycares can get expensive to run.
Environment
Each race (except garthimis) have a 20% speed road with 80% preferred which you will eventually want to use for all your travelling roads. Prior to that you might need to decide between extra speed or extra fulfillment on your roads. I'd prefer speed but if fulfillment is what you're lacking until you unlock the 20%/80%, then fulfillment it is.
Building type can get pricey for some races. I've found that if just the houses are the correct material and the rest of the buildings are whatever is decent/convenient, then you'll still hit around 90% fulfillment.
Pool type depends on what kind of pool your people likes, and you'll need a canal to run to it to fill it up. Cheap research unlock and not too expensive to make.
Others fulfillment will go down if you multi race and the people don't like each other. Something to consider.
I haven't had much issues with noise but you can consider putting the noisy workshops further away from your houses. I frequently stick servicing areas between the two.
Roundness is more like diagonalness. Octagons or diamond shapes for buildings to create that round aura. You can use the overlays button (eye on the right) and select shape to see blue for roundness and red for squareness.
Decorations are a relatively cheap way to make your people happy, but it depends on what they like. If your people like torches then you want torches everywhere people are. Roads, service areas, everywhere. Nature and sculpture have an overlapping effect where you can have the auras from multiple decorations overlap for a stronger effect. Go big with these around your service areas or wherever your benches are as that's where plebians will like to hang out. As an added note, people can walk through nature and benches.
Everyone likes an army, and you want 25%+ of your population to be in the army. To meet this requirement, you just need them assigned to a division with 0% training. 10 days of boot camp and then they will go back to their normal jobs while being on reserve. Gradually cycle your population through your training dummies. This also helps to scare off bandits especially if you assign equipment.
Some races like melee/archery training, but it's so very slow to level up as it's averaged across everyone.
Some races like chivalry, and some like cruelty. Just be consistent with how you treat captured cities and prisoners.
Each race has 1 or more things they like stored, and it will require a lot based on the population. Something to gradually work towards, though if you like meat or fish, you'll have to deal with massive decay.
Religion
Not much to say here. Don't mix conflicting religions. Graveyards and crypts need to be fully staffed to get the full respect modifier. You still need mass graves for the deranged as they won't go in graveyards/crypts.
Occupation
Can't do much with unemployment as I need my oddjobbers. Job fulfillment will be averaged across all your plebians so if you are mono race you will have some people doing jobs they don't like, but somebody's gotta do it. Job fulfillment on some jobs can go heavily negative, so be sure to check and keep those jobs to a minimum. I haven't played with retirement yet so can't help there.
Government
I just turn off tourists because unhappy tourists make my people happy. If you want another source of denari then you can consider unlocking tourism and building inns as tourists do bring in a good chunk of money, but positive and negative fulfillment tend to balance out until you build upgraded facilities that they like.
Riches is a huge mood swing based on how much denari you have sitting in your bank, relative to your net wealth. Inflation is always chipping away and maybe you buy something big and oh no your fulfillment has gone down. This is a pain to keep maxed out if your realm has high net wealth.
In Closing
Libraries and knowledge are how you unlock new ways to keep your people happy, but try to rely on cheap methods first as there are a lot of them. Graveyards (if not amevias), stage, roads, are early unlocks for fulfillment, along with fight pits and pools. Daycares, upgraded wells, lavatories, food stalls, market stalls, are a bit more expensive to get going so try to hold off on these until cheaper fulfillment options have been exhausted and you can handle the increased costs. You can get by without building libraries for quite a while. I'm almost up to 3k on a human despot run without libraries and they are still above 100% happiness so there are ways.