OTOH, if you just want to be a consultant who sells advice to startups, it shouldn't be much different than being a consultant of any other form. Hang out a shingle, work your network, cold call, etc., and convince people that you can help their company be more successful. If you can do that, you're golden.
That said, please don't do what so many people do... send out cold emails saying "I can help your startup generate more leads" where your own pitch email is worse than what I could write myself. Every "lead gen" firm that pings me sends me some mail-merge form letter crap that shows they don't understand rule #1 ("make it about the customer"), have done no research, know nothing about what we do, and couldn't spend 2 minutes personalizing their pitch. If that's the way you generate leads for yourself, no way in hell am I going to trust you to do anything on my behalf, ya know?