We are occasionally asked for advice about the worldbuilding process. By its creative and imaginative nature, the process of worldbuilding doesn't have a single obvious starting point or a step-by-step process that is universally applicable to all worldbuilding efforts.
The answer below lists many worldbuilding resources that can help you with your, "where do I go next?" questions. We recommend that you review these resources before asking us, so that if you do need to ask, you know exactly what problem you need to solve.
Please note that there are many specific questions assigned the worldbuilding-process and worldbuilding-resources tags. Most of them are too specific to be generally useful for the purpose of this post. We recommend reviewing them both for their content and to get an idea of the kinds of specific resource and process questions we answer here.
The answer has been created as a community wiki, which means everyone is invited to add resources. I and the moderators reserve the right to remove entries that we deem trivial or inappropriate. Everyone is welcome to help with formatting to keep the list neat and organized.
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Please DO NOT post additional answers to this question. Answers other than the community wiki will be arbitrarily deleted.
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Clarification: Due to James' query about whether or not it makes sense for this question to exist here on Main, I opened a Meta discussion asking why it shouldn't exist on Main. The post on Meta is NOT identical to this post. My personal belief is that this question belongs on Main.