Making an app window smaller on a mac

Well, there are some tricks in OS X Lion and above.

Since OS X Lion you can use any window edge for resizing.

If you hold down the option key, you can also resize a window by expanding or decreasing opposite sides of a window at the same time.

If you hold down the shift key while you expand or contract a window, the window will maintain its original aspect ratio.

Also you can combine option and shift.

If you want keyboard shortcuts (not built-in there) you can use 3rd party software like http://www.macupdate.com/info.php/id/26411/mercurymover.

If you don't mind using an add-on, take a look at ShiftIt. It allows you to use keys to move the window to left side, right side, top, bottom, lower left, upper right, etc.

https://github.com/fikovnik/ShiftIt

From the dev's website: