Set a campaign for website clicks.
Pick the correct device type (e.g. iPhones only for your iPhone experiment).
Don't make your targeting too broad - you will have a lot of Dropped visitors.
Don't make your targeting too narrow - you might get a really small amount of visitors per day.
Don't set a daily cap that is less than $200.
Target the users connected to WiFi in order to get less Dropped visitors (especially in Asian, African countries).
Don't add Audience Network to your placement - you might get 'wrong devices' in your experiment.
Don't make your ad banner look similar to just 1 variation to avoid the biased visitor's decision to install.
You might get a lot of Dropped visitors if you have already been using this ad banner for a long time. Try various ad creatives (static, video, banners that illustrate different features or show different characters etc.)
Add the store button to your ad banner.
SEARCH Page / TOP Charts / Multivariate test - make your ad banner generic (not revealing any of the apps that are there on the Search page).
SEARCH Page / TOP Charts / Multivariate test - make your ad text generic (e.g. Try out top 10 puzzle games), prepare your visitors to 'the list of apps' on your experimental page
Add utm-parameters (Example: ?utm_campaign=test&utm_source=FB) to the link for traffic in order to find the best performing audience/ad creative.