1. You should make your Adsense ads look as a part of your web page
2. Text ads are better than image ads
3. No Border ads
4. No other advertisements
5. Placement
6. ...

1. You should make your Adsense ads look as a part of your web page. They shouldn't look like an Ad. People are negative to advertising. They search the internet for content not ads. Especially Banners have a less of 0,5% response. Their days are over. Imagine if you have an Adsense ad looking like the typical Banner with different colors. It will not be profitable.

2. Text ads are better than image ads. Like before, people are more responsive to text than images..