The transition from graduate student or postdoc to tenure-track faculty member is hard. You discover that there are a ton of new things to learn.
Here are some thoughts on things to avoid.
You may see lots of ways in which your department could be improved; don’t try to fix all of them at once.
You may see needs for many new courses. Don’t try to develop all of them. Try to teach the same courses at least three years in a row.
Don’t agree to work with just any student who asks. While a good student can really help, a bad student can suck up all your time and energy. Students may be worried about money and feigning interest in order to get a research position, but if they’re not really interested, they won’t make much progress and it will be bad for both of you.
Don’t agree to collaborate with someone in the two weeks before a grant deadline. You might get stuck in a commitment with some total jerk. Find out if you’d really enjoy working with them, first.
Don’t agree to write a book chapter. It’s almost as much work as a formal paper, but not as many people will read it and it won’t count for much on your CV.