The Profiler window
https://unity3d.com/cn/learn/tutorials/temas/performance-optimization/profiler-window?playlist=44069
Diagnosing performance problems using the Profiler window
Physics Best Practices
https://unity3d.com/cn/learn/tutorials/topics/physics/physics-best-practices?playlist=30089
The Resources folder
https://unity3d.com/cn/learn/tutorials/temas/best-practices/resources-folder?playlist=30089
Assets, Objects and serialization
Fundamentals of Unity UI
https://unity3d.com/cn/learn/tutorials/topics/best-practices/fundamentals-unity-ui?playlist=30089
Other UI Optimization Techniques and Tips
Fill-rate, Canvases and input
https://unity3d.com/cn/learn/tutorials/topics/best-practices/fill-rate-canvases-and-input
Making the UI Backend Faster
https://blogs.unity3d.com/cn/2015/09/07/making-the-ui-backend-faster/
Optimizing garbage collection in Unity games
How to see why your draw calls are not batched in 5.6
https://blogs.unity3d.com/cn/2017/04/03/how-to-see-why-your-draw-calls-are-not-batched-in-5-6/
Unity 5: API changes & automatic script updating
https://blogs.unity3d.com/cn/2014/06/23/unity5-api-changes-automatic-script-updating/
Optimizing scripts in Unity games