To be productive with IntelliJ, you need to get used to working with it without touching your mouse/touchpad (or very rarely).

You want to be an IntelliJ Power User

To do this you will need to build muscle memory (or finger memory) for a lot of shortcuts.

The best thing to do, if you don't know the shortcut is to find it out, and use it immediately, and always!!

If you go back to the mouse and perform the action, undo it and do it using the shortcut.

The best shortcut to learn is Shift+Ctrl+A (for mac ⇧⌘A).

Sometimes, there is no shortcut, but just finding the action and doing it without a mouse is still better. You can always create a custom shortcut (will talk about this later)

Why?

This allows you to search for shortcuts. You just type in the action in the search bar and it will help you find the appropriate shortcut

Bonus:

Another reason I love this IDE. When starting out, you can hover the mouse over the tab or icon and it may tell you the shortcut too.