1. Your gut. Unless your gut is known for paranoid overreacting, you should listen when it's setting off alarm bells. If something doesn't feel right, or you experience inexplicable dread when you imagine yourself in the job, pay attention. Your subconscious is probably picking up on danger signs.
2. The job is over your head. You do not want to bluff your way into a job for which you aren't actually qualified. If the work doesn't play to your strengths, you'll struggle and could even end up getting fired. It amazes me how many people don't realize this.
3. You have a bad feeling about the person who would be your boss. The old saying that "people leave bosses, not jobs," is right. Make sure the manager is someone you'd want to work with.
4. The salary. On one hand, if you're unemployed, any salary is better than no salary. But if you accept a salary far below what the market says you're worth, you're likely to leave as soon as something with better pay comes along. That isn't fair to the employer, and it may burn bridges that you'll wish you had in the future.
5. The culture. If the culture is very formal and you go crazy when you're not in a relaxed environment, or if it's an aggressive, combative environment and you are more low-key and reserved, this probably isn't going to be a happy home for you.
You're going to be spending a large chunk of your waking life at this job. Be honest with yourself about whether you're going to thrive there.
Alison Green is the author of Managing to Change the World: The Nonprofit Leader's Guide to Getting Results. She is chief of staff for the Marijuana Policy Project, a nonprofit lobbying organization, where she oversees day-to-day management of the staff as well as hiring, firing, and staff development. Her writings have been published in the Washington Post, the New York Times, Maxim, and dozens of other newspapers. She blogs at Ask a Manager.