You can achieve this by using the Plugin [Peter's Login Redirect][1]. It allows you to send users to a specific page after login, based on the user capabilities. So you can allow administrators to go to the admin section, while members are redirected to the front page.

If you want to prevent users from ever seeing the admin, insert something like this to your `functions.php`, depending on which users you want to allow in the admin you may have to change the capability.

    if ( is_admin() && !current_user_can('manage_options') ) {
        wp_redirect( get_bloginfo( 'url' ) );
    }

You can also hook a redirect function to `login_enqueue_scripts`, to send every user calling the login page to the homepage (same structure as above).


  [1]: http://www.theblog.ca/wplogin-redirect