3 inter-related ideas that might help:
Chekov's Gun – a non-sequitor emphasis on any detail may signal to the reader that this will later be important to the plot. Worldbuilding is for writers. Too much can erode the reader's patience and muddy the story.
Characters observe things differently, and filter information through their own lens – a Biologist will view physical differences as deterministic ("The aliens have vestigial gills, therefore they are never far from a large body of water."), while a Translator will find insight within the language ("The Aliens have 17 different words for water, including some of their oldest-root words for God and Universe."), and an Engineer ("These extra vessels on their ship are designed to hold a gelatinous form of sea water. They can survive for decades hidden in isolation as long as the gel processors are functioning.") Think of the parable of the three blind men who touch different parts of an elephant and describe three different creatures.
None of your human characters will ever have a full understanding of the aliens, and they will always transmit their own biases while ignoring their blindspots. Every time a human describes an alien it should say more about that human character than the aliens themselves. The reader will perceive the aliens through a multi-faceted lens that doesn't fit neatly into a monoculture, and they will be forced to engage some imagination to bridge the descriptions. Moreover, the aliens will still have a mystery/other sense to them, and each new description offers a jigsaw puzzle of partial ideas rather than an infodump of factoids.
Combining the above can lead to "Ah-ha" moments in the story, when a character realizes what another observed (and described) that is outside their own experience. This gives you a plot-mechanic where it is necessary for humans to come together to discover something about the aliens, and a character can have a sudden change-of-heart or re-assess everything they thought they knew. These perspective changes enrich characters and prevent the story from becoming a travel log or descriptive wiki about your world.