Organizing CSS in large projects can be challenging, but following some best practices can help maintain readability and scalability:

1. Modularize your CSS: Break down your CSS into separate files based on components or sections like header, footer, navigation, etc. This makes it easier to find and maintain CSS rules. If you're using a preprocessor like SCSS, you can use partials to split your code into multiple files.

2. Use a CSS methodology: Methodologies like BEM (Block, Element, Modifier), SMACSS (Scalable and Modular Architecture for CSS), or OOCSS (Object Oriented CSS) provide guidelines for class naming and structuring your CSS. This can help keep your CSS consistent and understandable.

3. Use CSS preprocessors: Preprocessors like SCSS or LESS provide features like variables, mixins, and nesting which can make your CSS more readable and maintainable.

4. Comment your code: Especially in large projects, it's important to comment your code to explain what certain rules or sections are for. This can help other developers (or future you) understand the code.

5. Keep specificity low: Overly specific selectors can lead to difficulty overriding styles later. Try to keep your selectors as simple as possible.

6. Use a linter: A CSS linter can help catch errors and enforce consistent style.

7. Use CSS Custom Properties: Also known as CSS variables, these can help make your CSS more flexible and easier to manage.

8. Organize properties logically: Some developers prefer to organize properties alphabetically, while others group them by type (positioning, box model, typography, etc.). Choose a system that makes sense to you and stick to it.