One of the easiest ways to do this is to use BetterTouchTool. It will let you bind a keyboard shortcut or a trackpad shortcut to many commands, including maximize window.
Once you are in the BTT settings page, do the following:
- Go to the Keyboard tab on top.
- On the bottom near Keyboard shortcut, enter in whichever keyboard shortcut you want.
- For Predefined action, choose Maximize Window.
There are many other options related to maximizing besides "Maximize Window":
- Maximize Window Left
- Maximize Window Right
- Maximize Window To Bottom Half
- Maximize Window To Top Half
- Maximize To Next Monitor