You don’t want to put any cleaner or polish on your violin. It will usually make it sticky, and possibly ruin the varnish or the wood. This can affect the instrument’s sound as well. The best thing to do is keep a soft, clean cloth in your case or nearby, and gently wipe down the strings and violin top after playing. If the instrument is in bad condition, or the finish needs some tlc, it’s best to take it to a professional luthier for cleaning and polishing.