What are the key elements needed to create a great web application?
Using industry standard web framework such as Symfony.
Following SOLID, GRASP, DRY, KISS rules and using design patterns.
Testing during the development process with behat, phpunit and selenium.
Using of code analysis tools such as Sensio Insight, PHPMD, PHPCPD, PHPDCD, PHPCS and PHP-CS-Fixer to ensure high quality of the product.
This is how I work.
Knowledge of technology:
PHP - Very good
Design patterns - Good
REST API Development - Good