Below are the few things I found which can help to reduce rejection/pass EQP process.

 1. Keep Your vendor name same as **Vendor Name** of your Marketplace account
 2. Create your extension with `developer` mode enabled
 3. Must have composer.json in root folder of extension Eg. **app/code/Vendor/Module/composer.json**" with correct configurations and dependencies
 4. Must have registration.php in root folder of extension Eg. **app/code/Vendor/Module/registration.php**"
 5. Do not use `$_REQUEST`, `$_POST`, `$_GET`, `$_FILE` directly
 6. Never end class file with ending php tag `?>`
 7. Check extension functionality with Magento compilation `php bin/magento setup:di:compile`
 8. Remove unnecessary code and comments
 9. Use spaces for indentation
 10. Check compatibility with `production` mode enabled
 11. Test with cache enabled and disabled
 12. Validate your package e.g. `php validate_m2_package.php my-theme.zip my-module.zip`
 13. Check for code duplication [Refer][1] Use `ClassPreferences` and/or Magento 2's `plugin` structure to avoid duplicating code.
 14. Check coding standard with `phpcs` E.g. `$ vendor/bin/phpcs /path/to/your/extension --standard=MEQP2 --severity=10`
 15. Do not use `// @codingStandardsIgnoreLine` or `// @codingStandardsIgnoreFile` in code
 16. Do not use Magento logo in your documents or images
 17. Do not use "Product Box Image" as extension main image
 18. Add proper description for your extension functionality
 19. Correct grammatical errors (punctuation, capitalization, word usage, etc). Remember to use "a","an", and "the" correctly. Make sure words are plural when necessary. Be sure words that should be past tense are past tense.
 20. Do Functional/Unit Testing. as per @bhavani's [answer][2]
 21. Submit an e-copy of your Tax Forms to [email protected] (Required only if you are selling paid extensions)

 
Keeping the practice of following above standards will surely improve extension quality.


  [1]: https://magento.stackexchange.com/a/184417/2443
  [2]: https://magento.stackexchange.com/a/188075/2443