You can do something like this:
$("input").change(function() {
var inputs = $(this).closest('form').find(':input');
inputs.eq( inputs.index(this)+ 1 ).focus();
});
The other answers posted here may not work for you since they depend on the next input being the very next sibling element, which often isn't the case. This approach goes up to the form and searches for the next input type element.