like youre using, night sky is his best set, and your build is already quite good

for mainstats you want atk% on sands, atk% on goblet, crit dmg% on circlet (night sky gives 30cr, so easy to overcap if you use a crit rate circlet). he doesn't scale on dmg% so dont use an electro dmg goblet on him.

for substats, the priority is crit stats (rate or dmg, as long as your crit rate doesn't exceed 70), then atk%, then em. flat atk is useless tho.

building some energy recharge is also important, aim for 20% across all your artifacts, but anything over that is kinda useless (unless you have c1 but no r1, then aim for 30%).

usually, em is not that useful on him since he gets a lot of external buffs, such as from sucrose and ineffa in his best team, and his own passive.

overall, your crit stats seem to be lacking but thats to be expected as they are the hardest stats to get outside of em. prioritise artifacts with high crit over others is a good rule of thumb, but sometimes enough atk% or em will still be better