That is pretty straight forward, you use the login_redirect
filter hook which is there for exactly this case.
You would add something like this to your functions.php
file:
function home_login_redirect( $redirect ){
// Check if user is administrator; you probably want to redirect
// him to the dashboard, don't you?
if ( current_user_can( 'administrator' ) return $redirect;
else return home_url();
}
add_filter("login_redirect", "home_login_redirect");