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

# Module Checks:

 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**"
 
# Code Checks:

 5. Do not use `$_REQUEST`, `$_POST`, `$_GET`, `$_FILE` directly
 6. Never end class file with ending php tag `?>`
 7. Do not use `die()` or `exit()` in your code.
 8. Do not use `// @codingStandardsIgnoreLine` or `// @codingStandardsIgnoreFile` in code
 9. Remove unnecessary code and comments
 10. Use spaces for indentation 
 11. Check for code duplication [Refer][1] Use `ClassPreferences` and/or Magento 2's `plugin` structure to avoid duplicating code.

 12. Add PHP [DockBlock][2] for your classes

 13. Use proper DockBlock for each of your functions with parameters and return types.

 14. It is better to use [Service Contract][3] approach for your module development.

 
# Testing and Debugging:

 15. Check extension functionality with Magento compilation `php bin/magento setup:di:compile`
 16. Check compatibility with `production` mode enabled
 17. Test with cache enabled and disabled
 18. Validate your package e.g. `php validate_m2_package.php my-theme.zip my-module.zip`
 19. Check coding standard with `phpcs` E.g. `$ vendor/bin/phpcs /path/to/your/extension --standard=MEQP2 --severity=10`
 20. Do Complete Testing of your code. Execute command `bin/magento dev:tests:run` [More Reference][5]
 
# Content and Description Checks:

 21. Do not use Magento logo in your documents or images
 22. Do not use "Product Box Image" as extension main image
 23. Add proper description for your extension functionality
 24. 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.
 25. Check and confirm you do not have any broken link in your document or description content.
 26. Do not add links of other extensions/services in description content. **Promoting services or other created extensions in Magento Marketplace or Magento Connect is prohibited.**

# Other:

 27. 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]: http://docs.phpdoc.org/references/phpdoc/basic-syntax.html
  [3]: https://devdocs.magento.com/guides/v2.2/extension-dev-guide/service-contracts/service-contracts.html
  [4]: https://magento.stackexchange.com/a/188075/2443
  [5]: https://devdocs.magento.com/guides/v2.2/config-guide/cli/config-cli-subcommands-test.html