One of the more interesting parts of making up new intelligent beings, or new societies, is to think about language. Many science fiction stories and novels skip over these details entirely, because, well, they are hard. I've made my share of mistakes, and I know that I'm not anywhere near to getting as good at dealing with langauge as some writers. I think I suffer from being basically monolingual (unless you count programming languages). But I also do a lot of research, and that probably helps some. I'm not a linguist, though.
There are several layers to this. First, there are names. If you introduce characters who are alien, they generally have to be named in some way or another. The names have been, for me, an entre into what a language might be like. For instance, when I was writing my very first novel, The Casitians Return, I had to name this character who would become very central to the plot. Her name is Ja'el. I sort of did the apostrophe spontaneously (meant to signify a gutteral stop), and when I introduced other characters, most of them similarly got apostrophes in their names (although they don't all have apostrophes, like Silandra.) Later, of course, I found out this is somewhat of an over-used method in scifi (which is, I imagine, why I made the mistake – I'd read it so often.) But, by the time I'd heard that critique, I was done with the book, and on to its sequel, so I was stuck. So I just went with it.
In the Casitian Universe series, there are four languages represented: English, Casitian, Kinder, and Tud'scla (the language of the aliens that captured humans back in the neolithic age.) In a novel I have in progress, which is the story of the initial capture of humans, the Tud'scla invent a language that both they and the humans can speak. It is quite bereft of vowels, since they can't pronounce vowels very well. Example Tud'scla names include Hll'venr and Jrl'sen. Casitian and Kinder language are both descendents of that Tud'scla language, although the Casitian language has changed much more than the Kinder language – it has become much more fluid, and, as you can tell from Ja'el's name, pretty vowel-heavy. The Kinder got rid of the gutteral stop, but kept the lack of vowel sounds. An example Kinder name is Pkygy.
Anyway, that's a pretty simple set of things to create, and I think it mostly works, It fits in with the social structures of the Casitian and Kinder cultures, and their origins. That's the fun part – how do you weave in the language with the culture. Klingon (the language at the top left over there) is a great example of how this has been done.
I've made up some vocabulary terms (and I love making terms for things that don't have English equivalents), and names, but I have yet to think about actual sentence structure until quite recently, while working on another work in progress. The alien species in that novel (working title: Kepler Exploratory) has a language which has many fewer nouns and verbs, and a ton of adjectives and adverbs. In fact, for them, sentences can easily lack nouns and verbs and still be intelligable, unlike English. I'm still working hard on writing sentences (in English) which reflect the language. It's a tough one, but the language is a lot like poetry, and since I've written poetry, it feels doable.
I have yet to actually create a language. That is certainly not in my plan, but one never knows.