And honestly, I don’t know the answer to that exactly because it will be different for every license you give.
And different for every project you have.
And different for every licensee.
Some approach you, others you approach through meetings. So no right answer.
For example, you might have a really nifty young adult series with teddy bears, so you would research and set up meetings with teddy bear companies. But you wouldn’t do that with your tech-filled sf series. (Unless it was a very strange series.)
Robert Jeschonek wrote an amazing story about sentient underwear that was first published in Fiction River and then I bought it as a reprint for Pulphouse. Got a hunch that story will be reprinted a lot. That story might have some marketing traction in the apparel segment. Just saying.
So I think the answer is first, get ready. You need to know what your brand is, how to do an effective Brand Guide (Brand Style Guide), and the companies you want to partner with. In other words, research and learning.
Plus you need to have a lot of stuff under control and in place. The art, the publishing side, and most importantly your business.
And you need to make sure you are not hurting your own brands, or selling all rights for some stupid reason. The new world of writing stories is fantastic.
And without limits.
And honestly, I haven’t felt this excited about writing in a couple decades at least.