Just being around with my ears open I guess. Having the equipment to handle the work efficiently makes a huge difference when it comes to bid time. Talking with folks and hearing what they need/want is a good thing as well.
I got invited to the airport job because the manager knew me, although we haven't done work for each other. I made it a point to meet the engineer for the job and keep my name in the hat, so to speak.
Also, don't be afraid to do atypical work. Last year I filled a pool, best money I made all year. Just was in the right spot at the right time (2-4 years before we actually did the work.