I've tried to discern the context in which you're asking this question, but based on the OP and their replies, I think it's not so much about outlining than it is organizing details and thoughts before writing the initial rough draft. I might be wrong and that the OP‌ already knows about what I'd laid down below, but I hope even if it doesn't help the OP, it might be of help to someone.

Outlining is basically trying to organize your thoughts and all the details mapped out before writing. I assume that all the details are already laid out in one form or the other, and now it's time to put them into order. What order things would be put into depends on what is being described or being explained.

If I were to describe a house's interior, I might go from the main door, then proceeding as if I'm physically walking through the house, and then describing objects I encounter as if I'm panning the camera.

If I'm describing a person, I might go with the basic biographical details first, then an overview of their achievements, then personal life. Within each heading, for example, their personal life, I might go chronologically.

If I'm describing a process, I might go with an overview of what the process is for, what are its inputs, steps needed to prepare the inputs for the process, and then the process itself in chronological order. Within each step, I‌ might go into the reasoning behind having to do this step, or why this step must go before (or after) some other step.

If I'm describing an idea, I might go for a general definition first, then go more specific, discussing what makes each specific definition different from the others. I might then go for a quick historical overview of how this idea came into being, what ideas have led to this idea, and the thinkers that have contributed to building up this idea.

That is, there's a lot of approaches you can use to organize your ideas. You can organize your ideas or details based on location. That is, organizing details spatially, like describing a house's interior. You can organize your ideas based on time, which came first, which comes next, like describing a process. You can also organize your ideas from most general to the most specific (or vice versa, though starting with the most detailed first might require more concentration on part of the reader). One can use these and any other methods of organization you can think of so long as it makes sense given the context.

How you might organize your ideas or details would depend on what you're trying to achieve in the first place, and some methods are more suited than others depending on the topic. Lengthier works might even require a mix of these techniques. For example, if I were to describe a city for a D&D campaign, I might describe its layout first, laying out the details as if I were walking through the city. Then, I might describe its government structure from the widest in scope to the narrowest. Is it part of a kingdom? How is the city itself governed? Are there any districts, if so, how are they governed?. I would then give an overview of its history—in chronological order, of course. Any other detail that might be of use (for the DM or the players) can then be listed in order of most prominent or well-known to the least.

Now as a demonstration, I'll attempt to outline this response:

• Foreword and disclaimer
• Basic overview of outlining
• Examples
  • Describing a house
  • Describing a person
  • Describing a process
  • Describing an idea
• Organizing detail
  • Based on space/location
  • Based on time/chronology
  • Based on generality/specificity
  • Combination of approaches and others
• Demonstration