The best is to first define your niche, understand in which field you want to work actually, and then move out from there. Aim to find some niches that aren't so saturated and where there are some quality affiliate networks with decent commissions. Then, try to join those networks and contact them with an explanation of why you think you would be a good fit. It's desirable to have your own site or at least a landing page for this, or some developed social media with a high number of followers. Once you join on some networks, you have to work on attracting clicks to affiliate links and getting more monthly traffic to the site.