Honestly? Interview. A lot. I spent a couple of years interviewing in order to get better at interviewing (and always have my ear to the rail for better opportunities) and one of the side effects is that I met a lot of cool people doing interesting things. These people are absolutely a part of my network now, and I've referred at least one person to a job they got. It's a lot of work, but starting from zero, it is an excellent way to build a network, get good at interviewing, and most importantly, find a job you like that pays well.