Every Drupal developer should review this checklist
This list will be updated each time I remember something that you should know about Drupal. I strongly recommend that you refer to Drupal documentation and Drupal API list.
If you don't know it, you can synchronizing all your project environments to be identical by utilizing the config. Please refer to how to keep your local and remote site synchronized. I believe this is a must to do if you have more than one environment. For more details about this feature you can refer to Synchronizing Configuration Versions. Also, Managing your site's configuration.
You should get familir with the contrib module Views Bulk Operations (VBO). It augments Views by allowing bulk operations to be executed on the displayed rows. It does so by showing a checkbox in front of each node, and adding a select box containing operations that can be applied.
In order to be advanced user you need to utilize the existing power that you have with Drupal. And creating modals easily is one of the powers that you need to know that you already have it with Drupal. I encourage you to see how you can do that by visit this modal dialogs article.
I've seen a lot of Drupal theme, but it is not always what you see is built the right way. You should know how to include the needful libraries and how to reuse the existed themes to get the full benefit from Drupal theming.
To inline with DRY principle you should think of using Features module. And making sure that you can Exporting features. Fixing features conflicts.
One of the great modules is Organic Groups. Create Groups and Group contents. Make sure that you can Customize the access and allow group members manages the group contents
This experience will let you interact with Drupal in a new way. One of the great projects that you can play with is this one: https://github.com/jsdrupal/drupal-admin-ui