- Make extra campaigns per language.
- Use extra setting for only 1 cent per click for display networks.
- You sell a desktop app? Limit ad display to desktop computers.
People on a mobile phone are certainly not interested in your app.
- Don't send everyone to your start page. Point them right to the page they want to go. e.g. tutorial page for people looking on tutorial ad.
- Have lots of ad texts which contain keywords. Google prefers showing ads which match search criteria.
- Create several google accounts. This makes it easier for accounting the different ad campaign costs for different products or services.