On every window, there are 3 buttons colored red, yellow, and green. When you hover over the green, it becomes a plus sign. I want the keyboard shorcut for that. I know that cmd+w seems to be the red one. It does not always work but most often than not, it will close the window. Cmd+H is minimize. What is the third one?
You can assign a custom shortcut for the Zoom menu item in System Preferences:
Or if you want to always maximize windows to fill a screen, see this question.