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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
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

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