I did similar stuff for many years (and sometimes still do). By far the most effective was going and meeting people in adjacent or similar fields and making sure they knew about me.

My favourite was helping scientists - not the highest paying gigs, but the most interesting work and sometimes it led to great ongoing relationships as their go to tech person.

I would absolutely not offer freebies. That telegraphs desperation. Instead, offer a free initial consultation for a 1 hour meeting, and after that, they go into paid discovery at a lower rate than your full rate, out of which they get a technical persons documentation of the problem to solve. This approach definitely worked the best for me in the long run.