Here is a collection of useful game and scene optimization articles for Unity 3D.
Setting SpeedTree Up to Use Instancing – This tutorial shows how to set SpeedTree up to use instancing – this get’s you a substantial performance boost.
Optimizing Your Scenes for Mobile – This tutorial runs through how you can optimize your scenes for mobile games, with a focus on how to optimize your settings in Gaia.
Optimizing The Hierarchy – Best practices from Unity on scene hierarchy optimization.
Asset Bundles vs Resources – Learn about why asset bundles are better from the Unity team.
Why aren’t your draw calls being batches in Unity 5.6 – Learn how to minimize your draw calls with batching.
Unity Optimisation Part 1 for Intel x86 Platforms – The various profilers and how to use them to optimize your Unity performance.
Catlike Coding Tutorials – Some great tutorials in here