I have following code and I want to remove first seperator using css
here's the code

<div id="sub_nav">
| <a href="#">Fashion Insider</a>
| <a href="#">Leasing</a>

What do you mean...you want to remove this character "|"?

This is code I was getting on using wp_nav_menu in wordpress.
So i added seperator '|' into a span
Now it looks like

<div id="sub_nav">
        <span id="separator"> | </span><a target="_blank" href="">f1</a>
        <span id="separator"> | </span><a target="_blank" href="">f2</a>

Added css

#sub_nav span:first-child {
display: none;

And solved :)