(1) Learn more about the startup world (2) Help out some startups (3) Business development for new clients when they raise $ and can afford you.
The answer will depend on which one you're aiming for. My guess is that -- depending on how early the startups you're working with would be -- technical founders would end up looking to you as advisor on topics like negotiation, business development, and fundraising, rather than strictly legal advice. Generally after you help a startup 2-3 times they should give you some equity as an advisor.