[jQuery] how to use focus in a form?

well my problem is: I have n forms on the website that I working, then
I need one script on jQuery that's work in all using the focus to the
first element onf the form (excluding the firt hidden input), can
someone help me???, my starting code is here:
$(document).ready(function(){
if('form:first:input'){
$('input:first').focus();
}else {
$('select:first').focus();
}
});