Pep Talk - WHRN 2009 - Crimes of Information: How to get the most out of your infodumps and research by tiakall
It almost seems inevitable that worldbuilding and how to portray it comes up. You want to thrust the audience into a completely new world so it doesn't seem like "LA with fairies" or something un-unique, but at the same time you can't overwhelm them with detail. Too much and too little can both be damaging, so it's important to have a balance that draws people in without drowning them.
1. Separate the big details from the little ones. Big details are the things that are going to impact your plot, such as "This country is ruled by an evil king" or "The Hateual tribe attacks anyone that enters their territory", and those will obviously have to come out whenever the plot dictates. Normally if they're not too complex, they won't be that difficult, but infodumping can be a serious problem if you've got a lot to dump on the reader. If it's possible, the best situation is to spread out the relevant details over time to make it easier to swallow. (Aiganshen_Queen's pep talk will help you more with the issue of avoiding infodump.)
Smaller details are the ones that aren't important to the plot, but to the worldbuilding, such as "The southern people make tea from flowers" or "Pottery is the main export of the city of Polis." Right from the start, it's a good idea to sort out which details are likely to come up and which are just going to bog you down. It's impossible to fit in everything without boring the reader with all your "Look how much time I spent developing this world!" The right amount of small details is needed to make the world mesh.
2. Casual allusions and "Well, you didn't have to tell ME that". Details are like the word 'said', in a way; most of the time, you want them to be there, but not drawing attention to themselves or away from the story. Casual references are a great way to get those little details across, because those little details are very easy to relay.
Example: "Right now, she was one pissed-off botanist. It took her going through the sixteen stages of the kach's growth in her head before she trusted herself to speak." It gets across a small detail (that a kach is some sort of plant with sixteen stages of growth) while not detracting from the point (that that is one annoyed botanist). The details that are best included are those that have relevance to the characters in question (for example, plant-related details for a botanist).
Little details aren't the only thing that can be indirect. If it takes a whole scene to portray one plot-relevant detail, a quick infodump may be a better way to go, but often large details can be alluded to instead of being stated outright. For example, instead of saying that the place is ruled by an evil king, the main characters may hear some village peasants complaining about how that damned king has upped their taxes again and they'd give him a piece of their mind if it wasn't for the whole 'would probably be tortured and killed' thing.
3. What not to include, what not to change, and what not to say. In your enthusiasm to create a unique place, one might get the idea to go on a long list of reinventions of the wheel. For example, the local crop is ajils, a plant which is remarkably like corn, which is plowed by a apos, which is a plow drawn by a oich, a beast which looks remarkably similar to a horse. Most of the time there's no need to go renaming everything just for the sake of creating a "different" feel.
Generally, made-up words should be used if 1. there isn't a comparable or similar real-life concept, or 2. the language you're writing in doesn't have words that adequately cover the concept. For a real-life example, a lot of English adaptations of Japanese manga prefer to use Japanese suffixes when the characters address each other, because English does not have an adequate and succint counterpart for the social implications of using the various suffixes (or not using any). It's sort of like a pronoun for a concept in your novel, and should be used for things that are important and recurring.
Audiences will typically assume that unless you detail out that something is different, that things are generally the same on basic levels (for example: physics still applies.) Unless you have a plot-related reason to go changing the way basic human nature or science or so on works, best to leave it be.
4. How/when to research. Going off the previous idea, you may be well and content to keep things realistic, but sometimes you're not going to know exactly how physics or biology will work under certain circumstances (example: "How long can a person live when they've been shot in the throat?") Wikipedia and a good Google search are a great baseline to get some answers on, as most every obscure topic will be covered on the internet. While you do need to take Wiki with a grain of salt, it's going to be a lot more comprehensive than any local library. You may be able to find a book on cats at your library, but try finding one on main-belt comets. Wiki will also have more reliable links on scientific and technical subjects to verify your facts.
Surprisingly, another good place to look for an answer to the "is this realistic?" question is already-published media. While that won't answer the question directly, it will let you know if someone's already tried it and whether the suspension of belief held up, based on how the audience reacted to it. (I got a satisfactory answer to the "shot in the throat" question from CSI, of all things, after Wiki turned up dry.) It also gives you an idea of what not-necessarily-realistic things Hollywood and publishing can get away with (such as the idea of "I hit this person in the head to knock them out cold, and they wake up later when it's convenient with no brain trauma and only a mild headache.")
Small details are like spice: you want to use them to add flavor but not overwhelm the taste of the dish itself. And remember that it doesn't take a lot of spice to be captured to a galaxy far, far away.