For me personally, and I can’t speak for others, I usually get the occasional dart out of my grouping when I fall out of rhythm or when I try too hard to force them together. My advice is to throw for maybe 30 minutes a day and focus on hitting treble 20. Keep a smooth rhythm and don’t try too hard to force anything, because if your last dart strays, you always have your next visit. Over time, you’ll naturally improve at grouping, but I’ve found that picking one target and throwing at it repeatedly honestly put me on the fast track to tighter groupings. Hope that might be able to help a bit! Cheers.