Don’t be eager to know what THEY can do for YOU
You shouldn’t mention any of your demands (at least) in the first half of the interview if not directly asked about them. First, you should try to convince them about your serious interest in this job posting, in the firm, the workplace etc. and ask about things they need from you to be a good employee.
Don’t act arrogantly or self-conscious
It is tricky to balance everything out. Don’t boast or brag but don’t underestimate and demean yourself at the same time. Show you know about your qualities and skills but also mention you are happy to improve, accept feedback and put some extra work in.
Don’t speak informally or rudely
Even if the interviewing person acts friendly or very casually, you cannot take the liberty of doing the same. That means no familiarities, informal expressions, very personal information or even vulgarities you might be using among your friends from time to time.
No gossiping or complaining
First of all, never complain about your previous jobs, colleagues and bosses. Second of all, never mention any gossip about anyone, it is highly unprofessional and you cannot make yourself look better this way, only the opposite. There is probably no environment where this is praised or even acceptable and if there is, you definitely don’t want to work there.