Ways to keep dwarves happy:
* Juice up the dining room. All dwarves go there to eat meals unless they have a dining room of their own or they're soldiers set to carry meals with them. A high-quality dining room adds a big happy thought, and if you put lots of individual things in the room for dwarves to admire, that also helps (e.g. statues of varying materials, pointless weapon traps, a cage filled with every non-guard animal in your fortress, decorated ropes, etc.).
* Cook all your meals. If your dwarves are all eating raw plump helmet, then they aren't getting any nice thoughts from the meal and will eventually start getting annoyed because their meals are always the same. Switch over to quarry bushes and sweet pods and cook the meals; individual meal value will skyrocket, leading to more happy thoughts. Be sure not to run out of seeds (cooking plump helmets and berries will prevent you from recovering seeds from the plant), and don't cook your booze.
* Set up a mist generator. Dwarves love mist. And it stacks. A single mist generator in the right place can basically keep dwarves smiling through the apocalypse.
* Nice bedrooms. Setting up individual nice bedrooms is a real pain, but you can make a dormitory without too much trouble. Make a large room, decorate the hell out of it (like it was a dining room), and then put a bunch of beds in it. Designate rooms from each bed that fill the entire area. The rooms will overlap, so the quality of each bedroom is 25% what it otherwise would be, but it's not that much harder to make the room nice and you only have to do it once. This is somewhat exploity because overlapping rooms' values are not adequately penalized.