Be calm, cool and be yourself. It is a chorus with a verse but a greater tip many girls seem to ignore when trying to get over shyness with guys.
Here are further steps to take to overcome shyness around guys...
RELAX. Deep breathing is the first way to help yourself relax. Turn your attention to the guys, not your looks or your awkward shy feelings.
One effective weapon many girls use to overcome shyness around guys is joke. Crack a joke. Nobody wil ignore a clean joke. Nobody will be irritated, while you buildup confidence.
Ask genuine questions when things are not the way they used to be. For example, you can ask a guy what's wrong if he doesn't look cheerful or looks sick.
Wear clothes that makes you feel comfortable. Be decent. If you want to be shy and lose your confidence completely, wear skimpy dresses. A responsible girl will dress like a matured woman, knowing that reputation keeps you away from the shy feelings.