I haven't been playing DF very long, and my general strategy is to check my dwarves thoughts from time to time to see what it is they need. All but one are happy or better at the moment, but there are a lot of common thoughts:
If they're all happy or better, it doens't really matter too much at this point, though you are of course more vulnerable to tantrum spirals. That said:
* "tired of the same old booze". This is all very well, but my brewer keeps using plump helmets and we have nothing but dwarven wine. I have plenty of pigtails, enabled for brewing, which she could use, but I don't know how to instruct a brewer to use a particular plant.
You might try disabling brewing of plump helmets for a bit until you've got some variety.
When a dwarf works in a workshop, they'll try to gather the nearest proper materials first, disregarding z-levels. The problem is probably that you've got lots of plump helmets filling the corner of your food stockpile nearest your still, so those are chosen first, and are producing plump helmets too quickly so whenever a stack gets taken away another just gets put back into the same square, which then gets taken from again, repeat ad infinitum. You might try turning down plump helmet production to help fix that problem.
* "complained of crowded tables". This one's easy. There are only four tables in the fortress, one reserved for the bookkeeper, and migration has increased population to 23. Build some more, I suppose.
This one isn't due to not having enough tables (that is "complained of the lack of tables lately). "Crowded tables" means you're putting more than 1 chair next to each table. One table, one throne; more than one dwarf can't use a table at once. The solution is still more tables, but bear in mind that you can't put 4 chairs around one table, it doesn't work thay way.
* "annoyed by flies". This one's a real puzzler. I don't know how to deal with flies. My sole unhappy dwarf "absolutely detests flies", and I think this may be the reason for his unhappiness. Virtually every dwarf has been bothered by flies. How do I get rid of them? I have a refuse stockpile outside, and can't see any refuse lying around inside.
There's really very little you can do about flies. Fewer seem to spawn if your food is barrelled, but otherwise, there's nothing to do for it.
* "slept without a proper room". All the dwarves have a bedroom, and only a few are coming up with this one, but I can't figure out why.
It seems that dwarves can only sleep in beds that are accessible from the left or right (I just learned of this yesterday myself), so if you have, say, 3x1 rooms that might cause a problem. Also, are you sure you have enough bedrooms? Also, what version are you using? Many of the earlier 31.x versions had a bug where dwarves wouldn't sleep in their own beds.