Socializing And RelationshipsMany of the gameplay mechanisms built into the Sims engine revolve around making friends and building relationships. Although your Sim can lead a celibate, solitary life if you wish, it's preferable to have a large network of friends, even if you're only concerned about having a more diverse gaming experience. In practical terms, making friends is important due to the way that careers work: in order to get promotions at your job, you'll often have to have a set number of friends in your relationships menu.
Your feelings toward another Sim are placed on a point axis, and can range from hateful (-100) to deeply loving (100), with most relationships falling somewhere in between. One of the new additions in the Sims 2 is the Lifetime relationship score; your relationships are now based on both short-term feelings (the Daily score) and the Lifetime score. The Lifetime score measures the health of your long-term relationship, and thus won't change quite as quickly as the Daily score. Putting in the effort required to get a high score in the Lifetime relationship meter will give you new interactions, some nice benefits, especially for Sims with the Romance and Popularity Aspirations, and will let you bounce back rather easily from any social mishaps that might befall any given couple.
Meeting SimsIf you want your Sims to have a healthy and diverse set of basic acquaintances on which to base their friendships and loves, you'll need to get other Sims into your relationship database. You can do this by simply finding a Sim that you haven't met yet and introducing yourself to them. If an unknown Sim drops by your house (this will occur a few times a day, although the Sims that do stop by may already be known to you), you can make their acquaintance by walking out and greeting them; this will give you a basic relationship of zero points.
(If you ever feel that you need to make some new acquaintances, and don't want to wait for people to stop by your house, get your Sim into a good mood and head out to a Community Lot in the mid-afternoon. Depending on the speed of your computer, there can be as many as seven or eight other Sims in the community lot, randomly chosen from the inhabitants of the other houses in your neighborhood and some generic NPCs. This is a good way to make some basic acquaintances; try to build up your relationship score to the mid-20's with a few of them, if possible, if only to better the chances that they'll respond to a telephoned invitation to drop by your house.)
After you make a new acquaintance, you can start trying to boost your relationship score by interacting with the other Sim. This is accomplished by clicking on the Sim and choosing one of the social options from the pop-up radial menu. When you have a basic relationship of 0 points with a Sim, you won't have many options to choose from; in many cases you'll only have the basic Talk or Chat options. These basic interactions won't give you a super-huge boost, but they're good to use to get your relationship into the 20's or so, which is when more complex interactions become available.
It's worth noting that you'll only be able to tell how your Sim feels about another character, not how that character feels in return, unless you're checking relationships between members of the same household. If Joe Sim is madly in love with Jane Sim, for example, she won't necessarily feel the same way towards him. In general, though, these relationship scores are fairly analogous, so you can feel safe in using your own relationship scores as a barometer to gauge how the other party feels about you as well. Whenever you feel that you're using interactions that should be succeeding, but aren't, however, you may want to stick to some safer interactions until the other party is a bit more receptive.
Getting To Know All About You...After you get acquainted with a Sim, and have gotten a few relationship points with him or her, you can attempt to start building up a solid friendship. There are a huge number of possible interactions you can use in Sims 2, but you don't want to overextend yourself; if you try for a difficult interaction with a Sim your character barely knows, you're likely to be rejected, which will cause you to lose relationship points with that Sim and lose some of your Social Need, as well. It's best to be cautious with interactions by choosing the less risky ones until you're fairly sure that an advanced one can be attempted.
In general, the more romantically oriented an interaction is, the less likely it is to succeed with a Sim you're not friendly with. At low levels, things like Hug: Friendly or Appreciate: Admire are good ways to get some easy points. If you have a decent Charisma score, telling a Joke is also a good choice. Dancing is generally going to be the best way to boost your relationships without risking romance; the potential positive boost is more than double the negative penalty from a refused interaction.