try this
document.ready(function(){
$('#<%=txtusername.ClientID%>').focus(function(){$(this).addClass('glow');});
$('#<%=txtusername.ClientID%>').blur(function(){$(this).removeClass('text-label');});
});
<asp:textbox id="txtusername" runat="server" text="USER NAME" cssclass="text-label" autopostback="false" ></asp:textbox>