Giving your dwarves individual bedrooms helps, since they get a happy thought from sleeping in their own bedroom, and more happy thoughts from admiring the furniture they own.
The communal dining hall doesn't necessarily be huge, depending on your circumstances. I've found that digging a 7x7 unsmoothed dining hall in a flux layer, with a dozen chairs and a dozen thrones made from flux by a proficient mason, is often enough to get a legendary dining room, and you can make up the difference by smoothing and engraving.
Dwarves get a happy thought from drinking the kind of booze they prefer, so have a bunch of small/medium farm plots of as many different kinds of brewable plants as your can grow, including surface crops. You can gather from surface shrubs or buy plants from human/elven caravans and brew the results to get the seeds to start the process.
If you have a main meeting area, make it a zoo and stick in the cage as many different kinds of non-grazing animals as possible. Use cage traps to catch non-domestic wild animals, tame them, and stick them in the cage. You can also use animal traps to catch vermin and put the types that nobody hates (chipmunks, blue jays, etc) into the cage as well (vermin don't need to be tamed to be handled safely). Also, I believe that only
tamed grazers need to eat grass, so if a cage trap catches a grazer you should be able to simply install the cage with the un-tamed animal in the zoo and it will still generate happy thoughts.
Your central staircase (if you use one) should have its landings smoothed, engraved, and maybe in possession of a statue or two (I know some people like to add stuff like waterfalls, as well).
I'm pretty sure that smoothing and engravings aren't admired directly, but only act to increase the value of rooms (and the fortress). You can use them to increase the value of bedrooms, so they'll get happier thoughts from sleeping in them.