For me, it's usually a cup of tea. Quite often there's cake too.
That question comes from the Insecure Writer's Support Group and if you're thinking you never have much to celebrate, then perhaps you'd like to join?
We tend to think success means winning first prize, selling a story, or getting a publishing contract. Of course such things are wonderful – but that doesn't mean anything less is failure.
We won't win every competition or find a buyer for everything we write, but that doesn't mean we're no good or are wasting our time.
It's VERY important to recognise every writing achievement, even if it's just thinking up a good title, or spotting and fixing a potentially embarrassing typo.
If we've done better than that and actually finished something and submitted it we should definitely celebrate. (And do so again if the piece is bought or placed.)
What's your most recent writing success or achievement and how did you celebrate?