AdMob for Unity
How to Implement AdMob in Unity 3D – Interstitial Ad https://www.youtube.com/watch?v=q2eX2VMAYtA
How to implement admob in unity 3D: https://www.youtube.com/watch?v=Url91ixbTAY
Unity tutorial
Unity – Technical advices
Technical advices from our lead developer (formerly an app/web dev): https://madewith.unity.com/stories/5-lessons-i-learned-while-developing-our-first-game-flat-kingdom