Creating an original alien species is both important part in writing science - fiction stories (if you choose to use aliens) and a fun and interesting things in themselves. Some aliens are only to appear once, and play a moajor or minor role. Some are created to be a focus on the series, and some are in the middle. And some are msde for a single appearence, but the author then decide to bring them back... and expand them and use them more, give them point of views... And, finally, write a detailed backstory. This happened to many species I made, but, above all, to the Bohandi. The backstory can be read here:

https://docs.google.com/document/d/1xjKhBBZxcN3CVy9OVcdr9CZykWTIlwZVZ4yNpNPj3XQ/edit?usp=sharing

But this is not what I am here to ask you. I am here to ask you: how do you create alien species. And what do you consider to be the most important thing when doing so.