I wrote this:
a few years ago. As a co-founder of Masten Space Systems I would get this question frequently enough that I wrote a standard blog article about it. Here's the gist:
Work for NASA but leave before it makes you cynical.
Work in Mojave but leave or else you’ll never get married.
No matter what, build something.
Go to some key conference and meet people
Use LinkedIn, VisualCV, and yes, Facebook
Know your industry intimately
Join Students for the Exploration and Development of Space (SEDS)
Go get an advanced degree. Get it from the International Space University (ISU) if you can
Become an expert at something
Do something risky
Spectacularly fail at something
Be LOUD about it!