Note that if you already installed a submit event listener for your form, the innner call to submit()
jQuery('#<form-id>').submit( function(e){
e.preventDefault();
// maybe some validation in here
if ( <form-is-valid> ) jQuery('#<form-id>').submit();
});
won't work as it tries to install a new event listener for this form's submit event (which fails). So you have to acces the HTML Element itself (unwrap from jQquery) and call submit() on this element directly:
jQuery('#<form-id>').submit( function(e){
e.preventDefault();
// note the [0] array access:
if ( <form-is-valid> ) jQuery('#<form-id>')[0].submit();
});