As Legacy mentioned the job manager (u q) is your friend for some things. Very early in my fortress I queue up 300 render fat jobs. I do that as soon as the dwarf that does the manager stuff has bunches of free time. This is the best job for initial training of cooks.
Brewing drinks is something I handle manually because my farmers are also my brewers, and barrel requirements can be an issue. Cooking meals is handled manually as well. Much later in my fortresses when food, drink, empty barrels, and plants are at good levels; and all the dwarves involved have reached legendary status in thier professions, then I will let the manager take over for these jobs and I will balance it based on how many fields I mark for planting and animals for slaughter.
The largest way I handle idlers is with screw pumps. My fortresses have 4 worker groups. Furniture, food, woodcrafters, and pump operators. The furniture group includes all the miners, masons, mechanics, and metal workers; and tends to be about 15 dwarves. They can be idle as much as they want. Idling here means I have run out of things to construct.
The food union tends to be 6 or 7 dwarves. Two are trained as cooks, the rest are planter/brewers. By the time they are fully trained I don't mind them idling either, my food stocks are in the 10k range by then.
The woodcrafters make wood and bone bolts continuously. I let the workshops for these guys become heavily cluttered. If the military isn't using it up as fast as they make it then production slows down automatically which allows other things to catch up.
Finally we get to how the pumps are used. I like to call them dwarven tread mills. About 1/3 of each immigrant wave ends up working these, and this is my hauling force. This works perfectly fine early in a fortress as the dwarves will frequently stop pumping until they gain some skill, which let's them deal with the hauling tasks. Later when they have many stat gains, from operating the pumps, they get all the hauling done quickly. Anytime I need to free up more haulers for a sudden demand I just stop the pumps and they all immediately look for new work. This keeps them busy while still keeping that idlers number low. Since this group grows to a rather decent size I give them what I consider low demand labors along with hauling and pump operating. The list I use is butchery, tanning, leather working, weaving, clothes making.
If you still have large numbers of idlers then you should think about increasing the size of your military. I tend to draft 1/3 of each immigrant wave. You should see from the numbers above that I am fine with having 20 or so idlers when it is the right idlers. Those numbers are for a 200 population fort.