@ Thylacine
The good thing about writing a story is that you don't really need to deal with small talk all that much, since extended small talk is often about filling silence, so you can just cut out boring stuff in the name of good storytelling. You don't need to worry about being able to craft two hours of small talk between attendees of a baby shower, just a few basic things to get you to where you're going, y'know?
The first thing about small talk is that quite often people greet each other with "Hi, how are you?". And like 90% of the time when that happens the response is just "Fine/good/great, how are you?", but if the people know each other well enough, or something particularly big is going on in one person's life, or if they're just the type to overshare, it can be a place to expand a bit, and possibly bring you into some important information for the story, eg, "Hi, how are you?" "Oh, I'm okay, just a little tired. The baby was up all night." "Oh no, why?" "BECAUSE OF GHOSTS." Or whatever.
Topics of small talk tend to be non-personal life details ("Sarah started college," "We got a dog," "Jack started a new job at that office built on an Indian graveyard,"), the weather, ("Can you believe this rain?" "This heat is just unbearable," "I sure wish this plague of locusts would let up,"), and general but usually noncontroversial news ("How 'bout them [sports team]?" "Did you see they broke ground on that new building on main street?" "Did you hear about that zombie apocalypse they're having in Sheboygan?"). Often you can just gloss over the specifics with something like "They chatted about the weather for a few minutes before getting down to the business at hand: ghost zombies." It usually better that way 'cause readers don't really care about the weather/the athletic achievements of the son of a random minor character/the new Wal-mart that's opening up a town over – unless the small talk either a) reveals some hints about things relating to the plot or b) the two people exchanging small talk have some intense history, eg two people who loathe each other but are forced to exchange pleasantries for whatever reason, and in that case the characters' body language / internal thoughts are going to be a lot more interesting than whatever they're actually talking about.
Agreed with
shirtless on interrupting. It just depends on the people, the culture, the topic, and the power structure.
There's lots of cliches about body language, but they're cliches for a reason; mostly they're true. People cross their arms when they're uncomfortable or upset, clench their fists/generally tense up when they're angry, stomp around when frustrated, laugh when nervous/unsure (in like a talking-to-the-popular girl way, not a staring-down-death way), and tend to touch their face and/or hair around people they're attracted to. If you google "lying body language" you'll find all sorts of stuff about physical clues that someone's lying. There's lots of similar stuff about how to tell if someone has a crush based on their body language. You probably know more about body language than you realize; humans are social creatures so most people start imitating/learning physical social cues when they're babies. Even if you tend to be quite physically reserved, if you take note of how your body reacts when you're feeling certain things, you can extrapolate out how someone more demonstrative would behave when feeling that way.
Other general advice: The way people talk is going to vary depending on their circumstances and personality, but just about everyone uses filler words and weak language to some extent. This is especially true when someone's under pressure; that's why people who are usually perfectly articulate get up to do an oral presentation and suddenly are incapable of starting a sentence without saying "Um" first. Reading your dialogue out loud is great for checking the rhythm; if it feels stiff or is a tongue-twister for you, it's going to be the same for your characters + readers. It can also be a helpful exercise to practice conversations between two of your characters. If small talk isn't your thing, make them talk about their opinions of your favorite book, or what they think of a controversial issue, or what they think of another character. (It's also a good way to develop your characters' personalities.)
My goodness, that turned out longer than I thought it would. Hope it helps a bit.
) I would always let them finish what they're saying because I don't want to disrespectful.
