Best way to remove watermarks

[tiddles]

ok, one of our many new year's visitors did not use a coaster, and our nice walnut sideboard (one of our few 'grown up' pieces of furniture) has a white glass ring. Does anyone have a fool proof method for removing or reducing its visibility. I have googled and there are lots of solutions using abrasive materials - toothpaste or salt which makes me a bit nervous.

any advice gratefully received!!