As a Sci-Fi writer, I have given excessive though over the shape, temperament and environment needs of an alien being we might meet someday. There’s no reason to not have a billion different forms of life and limb, but some attributes seem likely to be more common than others. We are more likely to cozy up to aliens with the ability so communicate and that are not microscopic or gargantuan. They would be friendlier looking if not blobby or reptilian either.
If a planet has a sun similar to ours and the rocky planet is at a similar distance, many of the natives should have senses adapted to the available light and have body temperatures much the same as well. The basic 
quadrapedal plan might be a common solution, but not necessarily
. For a sci-fi book, nobody wants to meet the same old alien that looks like a guy in a costume. My favorites are the Falana here.
I varied a few parameters. The planet orbits a binary with greatly changing temperatures and gravity. These aliens will be rather resilient, I’d think. A soft body like ours would have a tough time enduring the rigors of annual variations in such an environment. I submit that a carbon rod shell to protect the tender body inside might be appropriate. And just because the vision should respond to a similar sun in a similar war does not mean the alien must have an eyeball. I gave the Falana eye stalks with different wavelength ranges for each sensor. They are two to three meters tall and can manipulate gravitational fields. Really handy, that.
Plus they are professional and respectful as well, as contractors out looking for work should be. Why not? I think civility in an advanced species is more likely than wanton blood-thirst. Besides, they would have alien DNA and our blood would be incompatible to their digestion.
How Would You Do It? 