Magento 2 frontend development can be really frustrating some times.

In order to ensure you can view the modifications of layout files folow the next steps:


1. Put Magento under development mode 
From CLI run command: php bin/magento deploy:mode:set developer

2. Disable Layout cache:
From CLI run command: php bin/magento cache:disable layout

3. Edit default.xml file:
- Copy default.xml from \vendor\magento\theme-frontend-blank\Magento_Catalog\layout\  to YOURNAME\YOURTHEME\Magento_Theme\layout\
- Make necesary adjustments to your layout.
- If the adjustments do not reflect in the frontend, run the CLI command: php bin/magento cache:flush

Note: the CLI commands are in Windows format (XAMPP). On Linux replace / with \ o paths