How to clear initial values in form text box on click

I have a "Contact" page with a form containing initial values for Name, Email, and Phone, and I want the initial value to clear when the visitor clicks on the respective text box.

I am trying to do something similar to the following:

<input type="text" onfocus="if(Email.value == 'you@yourcompany.com') {Email.value = '';}" value="value" />

Unfortunately, I have had no success with the following script in the "On User input" and "On Update" field actions.

if ( input.Email == "you@yourcompany.com")
{
input.Email == "";
}

Any thoughts would be appreciated.