Your SERIES-S doesn't require much maintenance, other than changing the coil every 5-10 refills. You can find out how to change the coil here.
However, it is recommended that you keep an eye on all of the connections and threadings to ensure that nothing becomes cross-threaded and that they are kept clean and free from debris or any buildup of e-liquid.
Also, if you experience any gurgling when inhaling, just hold the device by the battery and give it a couple of sharp flicks downward. You may have to do this a few times with a brand new S-Coil, but it will settle down with use.
Also, once every few weeks or when moving from a rich flavour such as tobacco, to a lighter flavour, you can clean the tank. To do this, open the tank as if you're going to fill it, and remove the coil. Rinse both parts of the tank in warm water, or leave to soak in a mug of warm water for 15-20 minutes and then rinse well. Leave to dry completely, install a new S-Coil, fill, and you're all set!