This is a related argument to the issue that if someone creates a “real” alien, it might be so far off from what human minds can comprehend that no reader or viewer could get into the story.
*headdesk* Do you have a cat? A dog? They are nonhuman, think very differently from us, yet most people have lived with one or the other. Consider our interactions with horses, pigs, ferrets, elephants, dolphins, parrots, etc. These are all animals we interact with. We play with them, train them, talk with them, eat them, ride them, occasionally even have sexual contact. My bet is that if we meet aliens, we're going to respond very much the same way: Can I eat it? Fuck it? Wear it? Play with it? Train it to work for me? Experiment on it? Decorate my house with it? Will it want to do any of those things to me?
This is why I often use animals as inspiration for an alien race. It gives me a basis of plausible biology to start with, and that suggests some things about its culture, how it might interact with people. The aliens won't think like humans, but will think as sapient beings. And humans will go right on being humans, the way we deal with the nonhumans we already know.
Another thing I do is bring in bits of far-flung human cultures, ones that many readers will be less familiar with than their local culture. That's because other humans are usually weirder than so-called alien characters. They have little quirks like Korean culture considering plans to be dangerous, or many Native American tribes counting a third (or more) gender, or the Canary Islands whistle-language Silbo Gomero. So make sure you at least out-weird other humans.
One of my favorite, most-alien characters is Alakazam by M.C.A. Hogarth. Imagine an empathic, fluffy person the size of a basketball who does not speak but does emote in helpful, usually pleasant ways and expresses preferences for certain people's company. Sort of like a pet, but always with a sense of being deeper, more nuanced, and ineffably mysterious. You don't have to understand it to like it.