The Formatter script automatically performs a number of common formatting operations.
To install, simply include this line in your monobook.js:
importScript('Wikipedia:WikiProject_User_scripts/Scripts/Formatter');
importScript('Wikipedia:WikiProject_User_scripts/Scripts/Formatter/Auto Edit Summary');
Make sure you refresh (Ctrl+F5) after saving to complete the installation.
When using an edit box, you should have a tab called format. Click this to use Formatter. Make sure you preview all the changes before saving!