Designing an Alien Species for Fun and Profit

For decades, science fiction writers and scientists alike have speculated about life on other planets. The possibilities they've come up with range from funny-looking humans (Thanks, Star Trek!) to completely incomprehensible horrors from beyond the limits of sanity (Thanks, H. P. Lovecraft!). This offers modern authors a wide range of possibilities to choose from, which can be liberating and terrifying all at the same time. On the one hand, the possibilities are endless. On the other hand... okay, where do I start?

Intelligence

 If an alien species is going to be a meaningful part of diplomatic negotiations (successful or otherwise), it's going to have to be at least as smart as humans. If it's going to be the one who seeks us out, then unless we already have FTL technology by the time of whenever the story is set, they're going to default to smarter than us. Why? Because the nearest galaxy is maybe a dozen light years away, and your alien species will need to have determined that there's something worth checking out on our insignificant little planet, or else they wouldn't have bothered.

That's not to say that individual aliens within your species can't be idiots. You get those all over.

Appearance

As indicated above, this can range from really really human to really really not. Many early aliens in visual media looked human simply because there was no such thing as ILM. In the Star Trek universe, most of the sympathetic aliens resemble humans with accessories because the Progenitor seeded a butt-ton of world with genetic material, and let evolution do the rest. Star Wars, being set in a space opera universe with a bigger budget, has a wide variety of aliens, made even more diverse with the addition of motion-capture and fully CGI sharacters. In written media, of course, you have a lot more freedom to make your aliens look like whatever the heck you want, but be cautious with aliens that are obviously not humans with weird makeup.

Non-humanlike aliens can even resemble familiar Earth species, like cat people (a favorite, for some reason), lizard people, or even insects. In general, the less mammalian they look, the harder it is for we humans to relate to them. Give them weird senses and a corresponding lack of familiar anatomy, and the average first contact team is going to be cautious, if not initially afraid of them. Once you start getting into the more mind-bending aliens like sapient colors (I have seen this played for laughs and for horror), it gets harder and harder to comprehend them, until you get the sort of things that should not logically follow the same laws pf physics, let alone biology, that we do.

Culture

Admit it. Coming up with a completely alien culture is hard as hell. Most fictional cultures will have some aspect of a familiar human culture, even if it isn't practiced openly, locally, or currently. This can be a good thing, if you want to use this fictionalized culture to make a social statement, but you will need to tread carefully and change things up. Transplanting an earth culture into your story wholesale can smack of lazy writing (no matter how awesome lion-folk Spartans would be). In general, your fictional species' culture needs to be an organic extension of the sort of environment they developed in, what they find important, and what they're naturally skilled at. That means you will need to build the heck out of their home-world and come up with a history for them, even if your human characters never find out much about it.

Mentality

Aliens are weird. They're supposed to be. Even familiar-looking behaviors and rituals can be performed for reasons that come completely out of left field, and understanding why can be a major part of the story (see Speaker for the Dead by Orson Scott Card for one example). Then you have the critters whose sense of morality is so completely divorced from ours that we have a hard time predicting what they will do any why, and they might have no concept of why what they did was wrong. Trying to weed out malicious behavior from attempts to help can be fun and horrifying by turns, depending on how you swing it. Try taking a quality and turning its importance3 up until the knob breaks, and see what that does to your creation's mindset.

In Conclusion

Creating a completely new alien species can be either piles of fun or an exercise in hair-tearing frustration. There's a lot of thought and world-building that can go into it if you want to have a meaningful first-contact scenario, but if you really get into it you can have almost as much fun working out the details of your species as you do writing a story featuring it. If you have fun writing about it, chances are your audience will have fun reading about it.