I may just be a hobbyist with a business degree and no entrepreneurial experience, Eosin, but here's some small tidbits of advice I can pass on:
1. Consider the customer. And by that, of course, I mean keep in mind the kind of customer base you want to cultivate with your products. Are you looking for enthusiasts that will embrace 3P's setting
en masse, discarding their old settings to use everything in your books and only what is in your books? Are you looking for creative types that like to skim off the top of various settings to make their own world and would pick up 3P's book to get new ideas? Do you want to sell primarily to DMs, players, or a mixture of both? The kind of product you release will largely be determined by who you believe your customer to be and what their demands are. Of course, who you
think your customer is and who they
actually are may be very different.
2. Consider the product mix. In the table top RPG industry, different types of products cater to different types of customers. If you boil it down to the basics, however, every book is a combination of crunch and fluff. Most campaign worlds are about 80% fluff and 20% crunch. The bulk of the rules you need are in the Core Rulebooks, you just spin new info around them. Of course, only fanatical gamers who love your setting will buy Fluff books. The more crunch you put into a product, the higher the likelihood that someone who doesn't play in 3P's setting will want the book anyway. This, of course, leads into advice #3.
3. Consider your competition. Investing in a campaign setting is expensive. Sure, you can drop $40 on the primary book, but if you
really adopt a setting, you're going to need to buy supplements on monsters, races, magic, and nations. What can you provide in your world that all the other companies cannot? What have other companies done that worked and what have they done that did not? Take, for example, the Scarred Lands. That campaign setting is a crunch fest, with each new supplement being about 60% fluff and 40% crunch. However, all the crunch is isolated from the fluff so that you can entirely ignore the world-specific information and use it anywhere. On the other hand, a setting like Dragonstar weaves the fluff and crunch together so tightly that it becomes trickier to use one aspect of the setting without using another. Obviously, the looser the setting, the easier it is for people to "sample" your world. But then you get caught in an endless cycle of needing loose supplements to keep up sales.
4. Consider using psychology. Marketing a product is all about getting in the mind of your customer and making them crave the product. How you go about doing this really depends on what you're marketing. Of course, one universal tactic that always works is the idea of "vested interest." Once a customer has a vested interest in something, they have a feeling of attachment and personal ownership that makes them want to look out for the best interests of the item in question. Take American Idol. Here you have a competition that routinely makes one or two pop stars a year. And their albums sell like mad. Because the public determines who stays and goes in the show, they feel like they have some active control over the career of the person. There is an attachement that makes the general public want to help the person along. If you can build an attachment to your world and products in people, they will support it. Sword & Sorcery did this through lots of open call work. But, let's be honest - that's expensive. I think this thread goes a long way toward building attachement as people get to see you in every step of the process. Just keep the lines of communication as open as possible on all levels and I think you'll get people interested. Of course, don't give away too much - that's not good for business either
Anyway, take what you want and leave what you don't. Like I said, I'm not expert. Just am armchair businessman wishing you the best.