We Have Met the Alien and He Is Us!
Okay Walt Kelly said it first. I went into some of the problems of designing a good alien and as I said it's hard. The good ones are all very different but with something that makes us want to relate to them. The mile long aerofauna of a Jovian world might be fascinating creatures but few would want to risk the dangers of descent into their hell world to carry on an exchange with any regularity. Maybe not. They might be the best mathematicians in the galaxy and able to clear up humanity's vague understandings of FTL navigation but you get the idea. On a more extreme case I have no idea how we'd interact with a super intelligent shade of blue ("Mauve! We require mauve to survive! You will give us your mauve or we will inflict plaid upon you!".) Can you trust that marker? True it is labeled cobalt, but I digress. An easier technique is to take humans or uplifted animals and give them some new tweak or development that makes them alien in some way. I already went