first of all i apologize for my bad english.
Ahri is not very strong in the early game. So follow the map and the jungler well and if the fight has started somewhere, try to get there as soon as possible. If you fall back, stop playing aggressive, try to farm and wait for the jungler to come. Since Ahri's W ability instantly gives movement speed, you can counter incoming abilities.

Ahri is really strong in the middle game. If you patiently wait for the midgame and you have at least 1400/1500 gold, it will start getting stronger quickly. You can try to gain an upper hand by using your power in the middle game. But remember, don't stop being careful as your opponent grows stronger with you.

Ahri is a character that falls out of the game, albeit a little in the late game. Not as strong as in the midgame, but not as weak as in the early game. Try to get the carriers out of the way with your R ability in teamfights. But use the 3rd R to escape. If you get caught alone, either try to escape or fight them if the possibilities are right and stall until your team arrives. Try to protect your ADC as Ahri is a little tank character in the late game.