I’ve learned that 1) it’s easy to overvalue your own contribution to a project, and 2) it’s important to file a written status report on projects and activities with your manager on a weekly basis, even by sending a weekly e-mail that says “here’s what I accomplished this week.” 3) If your manager is taking credit for your work, their job is not to actually do work themselves, but to manage people to get the work done. So if you complete a project, and your manager gets credit, remember that his job is to have you do the work.
Seriously, people above you have no idea what your individual contribution is, unless you stand out on one high profile project. I’ve gotten good mileage out of a good “elevator speech” When I get on the elevator with senior management, I comment on how excited I am to be at work and the project I’m working on. They always brighten up, ask me what I’m working on, my name and my manager. After the first time, when we get on the elevator, they ask me what I’m working on now.