Qn: How to clear a text in text box on amouse click after page loaded

i used this code   onclick="this.value = '';"   in the  tag 

it worked successfully , on the mouse click text box cleared.But the Problem 
is that when i insert values to the text box 

and mouse click for further editng cause the clearing of the text box

Thank you

Best solution would be to use a javascript if you want to clear the text 
in a textbox when a user clicks on the textbox.