This tip and trick is something I find very useful when working with web parts and widgets. You are probably aware of the dialogs that you get when adding or modifying web parts and widgets. These dialogs consist out of default properties which apply to all web parts and widgets and some custom properties which can be set per web part and widget.
 

Kentico adds the default properties via a couple xml files which can be found at the following locations:

With these xml files you can easily add, modify or remove the default properties. This is where you can find properties like the title of the web part, the hide on sub pages checkbox, display to roles selector and the html envelope with the content before and after fields.