How does Apple count app downloads? If a user downloads a game but then deletes it, does it still count as a download?
Will if affect the ranking of your app?
Yes, if the app is deleted after being downloaded, it still counts as a download. Deleting the app does not affect the ranking of the app.

If you download the app over and over again using the same Apple ID, it will still count as one download. You cannot improve your rating by downloading the same app over and over again unless you use different Apple IDs.