Is there any easy way to clear up paint 'dribbles'?
Unfortunately I've never been able to find a satisfactory way other than "sand it down and start again".

The only upside is that you should only need to sand down the affected area and repaint that. The paint is new enough that there shouldn't be any difference in the colour and with care you should be able to feather in the patch.

As you are painting over tiles, you might be able to get away without any feathering - just sand all of the affected tile and then when you repaint take care not to touch the adjoining tiles.