Remove any PHP or JavaScript code after the "value" attribute of your HTML form for the input field that you want to remain blank.
// if you have this:
<input type="text" value="<?php echo $value; ?>" />
// change it to simply this:
<input type="text" value="" />
// or better:
<input type="text" />
You don't have to remove or change other attributes ("name", "id", "size", "maxlength", etc.).