IMO in terms of making the best impression when joining a new project: Docs are a huge one. I think people always wish they had better docs, and when new folks come in and show they have the discipline to contribute in this area it goes a long way in building trust.
At the risk of being overly pedantic, when people say they wish they had better docs, what they are really wishing for is more effective ways to communicate and share understanding... documentation is a way of achieving this end, but we need to keep the end game firmly in mind to be able to solve this problem in other ways.
But to add something more constructive to the question, the big things I'd want to understand is:
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.