I wish I had more seriously considered what mattered to me most in a job: Would it be a flexible schedule? Ability to do procedures? High pay? Working with excellent colleagues? Hiring my own staff? Having a relationship to a highly respected hospital or higher institution?
I also wish I had known that when finally looking at my first contract, the most important part is how I would get out of it. Most people do not end up permanently at the first job to which they are hired.
Finally, I wish I had known that interviewing for an attending job is the opposite of interviewing for residency. The supply and demand curves are finally reversed and in your favor. Remember, you are a highly valued commodity, so you should feel comfortable asking for what you think will make you happy.