HungerHunger, obviously enough, is replenished by instructing your Sim to sit down and eat. It sounds simple, but Hunger will often be the most aggravating Need to fulfill, if only because it takes a rather long time for your Sim to prepare and eat a full meal (on the order of an hour or so), which generally won't even fill their Hunger bar all the way up. Luckily, the Hunger motive decays less quickly than do other motives, so one full meal a day should be all you need to keep your Sim up and running.
There are a lot more food options in Sims 2 when compared to the first Sims, but the same basic choices are still around: you can instruct your Sim to grab a full meal (which requires preparation and is very filling; there are recipes you can choose between this time around), a quick meal (which doesn't require any preparation, but isn't as fulfilling as a full meal), or to call for delivery, which doesn't require any preparation, but will take a while to arrive and will cost money. Alternatively, you can instruct one of your Sims to Serve a meal; they'll make a number of servings of whatever recipe you choose, which your other Sims can grab and eat without any prep time whatsoever. The individual servings here are a bit less filling than full, self-prepared meals, but the time savings are generally worth the effort. Serving is especially useful when you have large households and can rangle everyone into the kitchen at the same time, as everyone will be able to socialize at the table while they eat. If one of your Sims has a high Cooking skill, they'll be able to provide everyone with a nutritious meal, letting each other member of the household move on to more pressing Needs and Wants.
Sims that attempt to cook a meal when they have a low Cooking skill score may start a fire in the kitchen; the resulting trip from a Fireman will drain you of a bit of cash. It's safer to learn Cooking from a nice television or from a bookshelf; when you reach rank one or two, you can try again with less fear of failure. Microwaves are also unblowupable, so they can be used in place of a stove if you're afraid of fires. (Or if a Fire is one of your Sim's Fears; in this case it's best to stick on the safe side and avoid stoves if your Sim is a poor cook.)
Needless to say, a low Hunger Need is a bad thing for any Sim to have; if it drops all the way to the bottom of the meter, your Sim will starve to death. Luckily, there's an incredible amount of leeway in terms of getting some food for your Sim before this unfortunate eventuality occurs; your Hunger meter will usually drop almost to the bottom, then stay there for as many as 12 hours or so, giving you plenty of time to prepare a meal or ten before time's winged chariot swoops down to pluck you from this mortal coil, etc. In short, it's difficult to die of starvation unless you're actively trying to kill off one of your Sims.
For more info on efficient food preparation, check out the Kitchen section of the Building Tips chapter of this guide.
FunAlthough your Sim needs the basic necessities of life, like sleep and food, he or she also desires the intangibles, such as Fun. This is usually combinable with Social, in that many of the objects that work to increase your Fun score can be used by more than one Sim at a time, allowing you to gain Social, Fun, and perhaps relationship points all in one fell swoop.
The classic Fun item is the television. If you place a television in front of a couch, two or three Sims will be able to watch at the same time; they'll converse about the program they're watching, while gaining Fun, Social, and Comfort from their sitting arrangements. (The safest channel choice is usually SBN, which teens, adults, and elders all tolerate. Kids won't like it, but there should be fewer of them than any other age group.) The more expensive the television, the more Fun that you'll be gaining.
Another good option are the game systems. Both the Maxis Game Simulator and the It's MYSHUNO! game will give you an excellent amount of Fun and Social, as well as Comfort, if you place them near good seating. If you have to play them solo, one Sim can use them to gain back Fun, but this obviously won't improve your Social Need at all.
Dancing is also a good source of Fun, especially at parties, where you'll need to gain plenty of relationship points in order to have a successful shindig. Dancing with other Sims gets you plenty of relationship points, so you should make this the focus of your parties; get a good stereo system, along with plenty of speakers, and you should have plenty of room in which to dance the night away.
EnergyEnergy is the one of the most straightforward Needs in the Sims 2. Every Sim needs to have a little get-up-and-go in them, or they're prone to poor performance at work and unscheduled napping. If you let your Energy fall too low, in fact, your Sim will drowsily shrug off all of your commands and fall asleep on the floor! The solution, of course, is massive infusions of trucker drugs.
Well, no, it isn't; what your Sims need is sleep, and plenty of it. Sleeping requires a lot of time, and it obviously disallows any other actions on the part of your Sim, so once a day you'll need to drop what your Sim is doing and shove him or her off to bed for eight hours or so. There are other methods of supplying Energy, notably napping on a couch or drinking espresso, but these are uniformly inefficient when compared to some solid REM time. Energy will drain at a fairly good rate during the day, no matter what you do, but, again, there's not much you can do about it except to just take the mood hit and focus on your other Needs. If you really need to get your Sim in a good mood for a special occasion, such as a party or an important romantic proposal, try to get some sleep immediately beforehand to ensure that your Energy Need is well satisfied.
One thing to take note of is that your Sims will often stay in bed even after they've reached maximum Energy. They will get up eventually, of course, but if you want to reach maximum efficiency, you'll want to monitor your Sims as they sleep and prompt them to cancel the sleep action when they've topped off their Energy bar.