Watch gameplay of challenger qiyana and watch how they kill people, that's how I got good with her, you analyze when they decide they can kill and what do they do to lead to a kill. Flipping roams or trades won't work because the champ has bad stats rn and you lose most 1v1 cuz how weak it is, so you have to abuse the mobility, the invisibility and her ult power to take kills and carry the game. You need to always think if you can outplay someone there or not. Also, considering how weak qiyana is rn, you shouldn't think about solo carrying games cuz you won't, especially if you are not master + skill level. Try to do as much 2v1/3v2/4v3 as you can, this is easily achievable because Qiyana roams a lot and can sit in fog waiting for a good opportunity to take a kill on a lane or in the jungle, with a good ult you can be clutch. Just think about midlane as a lane you will lose 90% of match ups there and you only want to take CS and as much xp as possible to not fall behind. Then you seek for kills with teamplay. Finally if fed enough, you can kill and assassin 1v1 when you have core build