Having to scroll back and forth over unused applications on your Blackberry will wear out your thumb. Place your most frequently used applications close together on the home screen to make your life easier.
To move an application icon on the home screen of your Blackberry, roll over the application, press the Alt key (the one that looks like a crescent moon) and click the wheel. Select Move Application, and roll the wheel until you find the right place for the application. Then press the wheel again to put the application there.