If you think you’ve neatly defined all the boxes that posts will fall in, you can disable the Uncategorized category in /admin. The setting is called allow uncategorized topics. With uncategorized disabled there is no default category, users will then have to pick a category for every post, which makes mis-categorization unlikely.
Renaming Uncategorized had the potential to create confusion, and is no longer possible. Personally I only leave it enabled to encourage users to post even if they can’t see somewhere the topic will fit.
We spent quite some time to think about our categories. And “General” will probably be the default category to choose from, for the most hesitant user.