Background: ~30 y/o, work 9-5, make slightly less than 100k/yr, not much in savings (outside of retirement accounts), $25k student loan debt remaining, no other debt, rent an apartment

Question: How to start generating passive income, or in my case, more realistically, best options for side income (not strictly passive)?

Yes, I know, this is like asking "How can I make a million dollars real quick?" But honestly, I don't know where to start. Are there any books or websites you recommend for tips on generating supplemental income? Figured I'd ask here as it seems like the crowd here would have some experience in this, and I'm still just brainstorming.