The Best Way to Add Custom JavaScript and jQuery to SharePoint

During extensive SharePoint user interface customization you'll likely encounter a scenario where you need to make a web part or user control do something it was not intended to do or have a look that cannot be accomplished using the CSS hooks provided out-of-the-box. The solution is to create a custom master page and include a reference to a JavaScript file where you can modify the Document object. While straight JavaScript will do, I prefer to use the jQuery JavaScript library, which is far more robust, easier to use, and allows for plugins. Follow the steps below to add jQuery to your master page.