What symptoms do they show before they die? Anything unusual? Did the dead fish have any marks on them?
Where did you get them? Were they showing anything unusual then?
Does he look like he's stuck upside down, or is he just swimming upside down?
What are you feeding them?
What are your water parameters? Ammonia, nitrites, nitrates, PH?
What else is in there? Anything that could possibly be aggressive? Anything large?
Any sort of chemicals used near the tank? Aerosols of any sort? Did anything in the tank have any sort of soap on it?
Any newly added plants that can't be IDed?
I hate hearing people say "it's only a $3/$5/$1 fish/shrimp, so it's ok if it dies, I can just get another." It's still an animal! All animals should be treated like they're worth $10,000.
29 sw: Damsel, shrimpgoby, pistol shrimp, waspfish
65 fw: Rummies, glowlight tetras, pencilfish, darters, ottos, f betta, goby, dwarf gourami, ninjas
29 fw: Chili rasboras, pygmy cories, P. Gertrudae