What do you wish you knew about your job when you first started out?
Senior Software Engineer in Okemos:
"Get Out Of Debt."
Get out of debt as quickly as possible. Start maxing out your 401(k) (or equivalent) when you're young so you get used to saving for retirement.
Senior Software Engineer in Beaverton:
"Recycled Code By Dilbert."
It is rare to work on a truly new project. Most projects are variations on an existing product, and much of your time will be delving into pre-existing code (usually poorly written) to fix problems or modify it in some way.
This is not necessarily all bad. The work can be very challenging, and you often learn new tricks or ways of doing things.
Much of your time will be spent in meetings, where insignificant details are debated for hours. Dilbert accurately portrays an engineer's life.
Senior Software Engineer in Seattle:
Don't be shy, keep your ears open and talk to coworkers about the problems they are working on and offer any insight you have and accept any they may have for your tasks.