Approaches to finding potential collaborators and co-authors
Here are a few key observations I've made about the process of starting collaborations:


Most people one would like to work with are already quite busy, and have many random people come to them looking for collaboration.  If you want to be taken seriously, you need to have a specific and detailed idea of a way that their work can make a difference to your goals or your work can make a difference to their goals.  Once you start discussing, you might end up somewhere totally different, but clear and specific thinking is key to getting things started: I suggest Heilmeier's Catechism as a useful framework for your thinking.
Most collaborations thus start with a discussion with between PIs, but are only fully realized if a graduate student or postdoc becomes involved to do a lot of the work.  Early career researchers may play the role of both PI and postdoc themselves.  Be careful, however, to keep acting as a collaborator rather than turning yourself into a free postdoc.
Almost no interactions turn into collaborations.  A good rule of thumb is that for every 10 people you meet, 1 will become a potential collaboration; for every 10 potential collaborations, with 1 there will be meaningful follow-through on the possibility, for every 10 with meaningful follow-through, 1 will actually turn into a significant collaboration.  Don't get discouraged, but also don't waste time pursuing people who indicate they aren't interested beyond the point you are at.