SocialYour Social Need is similar to Comfort in that it will likely be satisfied in the course of your everday activities. Since the Social meter is boosted by interactions with other Sims, most of the Sims in the game will keep their Social Need almost full just by going about the process of fulfilling their Wants. The Popularity, Family, Growing Up, and Romantic Aspirations are full of socialization-based Wants, and even the Knowledge and Fortune archetypes will see their fair share of interactions pop up, especially if you can manage to get the Sim to fall in love with another character. If you can feasibly go after these Wants, do so, as you'll be giving both your Social meter and your Aspiration meter a boost at the same time.
If your Social motive falls too close to the bottom of the bar, your Sim will begin hallucinating, which will create a magical Social Bunny which will attempt to cheer your Sim up by offering a few special, high-Social interactions. None of the other Sims in the household will be able to see the Bunny, so they may consider the fact that your Sim is talking to nothing a tad odd, but they obviously don't care so much about your Sim anyway, if they let his Social rating get so low in the first place.
EnvironmentEnvironment is the Need that is the most difficult to directly influence. Your Sims are attentive to the environment around them, and prefers to dwell in comfortable, attractive surroundings. Their Environment score will reflect this level of satisfaction, for better or for worse; if you plop them down in a bland hovel, you can expect them to be distinctly depressed about their residence most of the time. You'll need to spruce up their living area with decorations in order to make them feel better about where they live.
In the early game, you can help your Environment score by instructing your Sims to clean up after themselves, as overflowing showers and dirty plates stacked up on the kitchen table will quickly begin to offend them. (You can also hire a maid via the telephone to clean up your residence.) This is only a bandaid effect, though, as you will never be able to bypass the maximum Environment limit that's set by the quality of your items, no matter how obsessively you polish the silver. As such, Environment becomes the money Need in the mid-game (if such a term even applies to a game like the Sims): the more disposable income you have, the easier it will be to buy the expensive decorations required to appeal to your Sims' sense of aesthetics.
Before resorting to pure decorative items, though, you should scout through the catalogs to find items that have Environment boosts tacked on to more utilitarian purposes. For example, many of the more expensive seating options will have the same Comfort scores as the more thrifty choices, but will also give your Sims something to admire from across the room. Some consumer electronics, such as big-screen televisions, will also have appreciable prettification factors. Non-decorative items that add to Environment are generally quite expensive when compared to purely utilitarian choices, though, so you may want to just spend your cash on simple decorations.
Decorations come in many different forms, although the "best" are those that can fulfill your Environment Needs without taking up precious floorspace. Paintings are obviously great for this, although they can be quite expensive for the amount of Environment that they supply. You can expect to pay over 100 Simoleans for each point of Environment that you gain; some of the more reasonably-priced items are Transcendence by Joan Schnitzel (6 Environment for 800 Simoleans) and The Meaning of Fruit (10 Environment for 1,500 Simoleans). (These are easily found in the menu due to the fact that they're the only paintings that feature bowls of fruit on them.)
Sculptures are also a good choice for Environment, although they as well will be somewhat inefficient for Environment, especially towards the more expensive end of the spectrum. The Pink Flamingo no longer gives Environment bonuses, unfortunately; the cheapest option for that now is the yard Gnome. A better choice here is the Immobile Chimes Mobile In Steel sculpture, which offers 10 Environment for 1,500 Simoleans, but which will take up a few squares of floor space.
Lastly, note that Environmental scores outside the home are judged in small areas; there isn't one Environment score that will affect the entire outside of your home. For this reason, you'll want to have the area near where you hop onto the schoolbus or carpool the mostly brightly decorated part of your yard.
HygieneHygiene, like Bladder, can be raised from low to full quite quickly. It will lower naturally over the course of a day's exertions, but your depletion rate will accelerate when you perform strenuous or messy activities, such as exercising, eating, or going to the bathroom.
The simplest way to refill your Hygiene is to take a shower or bath. A shower is usually the quickest way to get your Hygiene back up to spec, but these have a tendency to leak all over the bathroom floor, harming your Environment Needs, and don't give you the bonus Comfort that taking a bath does. In general, though, showers are still preferable to baths, if only because they do save time, the messes are easily left for the maid to clean, and the lost Comfort when compared to a bath will easily be made good when you hit the sack.
Since your primary source of Hygiene penalization will usually involve emptying your Bladder, it's best to save your Hygiene replenishment until immediately after you use the bathroom. Most bathrooms in the storymode will come ready-equipped with both a toilet and a shower or bath, so it's not difficult to instruct your Sim to do one and then the other; afterward, they should have these two Needs satisfied for the rest of the day.
This doesn't mean that you always have to satisfy your Hygiene score after you relieve yourself, obviously; you'll likely want to have your Sims make a quick trip to the bathroom in the middle of the day to boost their Bladder, but it's not often worth the time investment to take a shower afterwards. If you do manage to top out your Bladder sometime in the afternoon, you can generally save your next bathroom trip until you get out of bed the next morning. A morning routine of waking up, using the bathroom, and then showering is the best way to ensure that your Sims have a good head start on the rest of their Needs.