HTML/PHP - default input value

I have a post php form and a set of inputs:

1. Your Name
2. Your Last Name
3. My Name

Every input looks the same, only the names change:

<input type="text" name="your_name" value="<?php echo get_option('your_name'); ?>" />

How to set default values when value= is not available?

[edit]

Ok, so, normally I'd do something like:

<input type="text" name="your_name" value="Mike" />

But in this case I have a PHP script that grabs inputs data and displays it using value="<?php echo get_option('your_name'); ?>" . So I have no idea how to force my form to display "Mike" in my input.