In order to get more quality users, you need to sharpen up your campaign’s targeting:
Your users will be more likely to install your app whether they are using their phone or tablet (reasons: app weight, purpose of the app, gameplay,…). You can do some A/B testing and create 2 different campaigns to see how the results differ, in terms of performance and KPIs. You may also create specific sets of creatives, showing a smartphone or a tablet according to the device(s) you want to target.
Targeting a higher OS version will increase the percentage of paying users, especially if your app requires a high-end device to run smoothly. You may create different tracking links per OS version. Once you get the first results, apply a specific CPI per OS version. You will typically choose a higher CPI on latest OS versions (for instance, 5.0+ users on Android and 9.0+ users on iOS).
If your app weights over 40Mo, we advise you to consider targeting “Wi-Fi-only” users. The best way to start is from A/B testing: create 2 different tracking links, one targeting 3G users and the other one for Wi-Fi only. Only keep separated links if you see a significant difference in terms of results.