Need optimizing tips for mobile third person shooting game.

I am working on a third person shooting games for mobile.

I need some optimizing tips for the same.

For eg I read somewhere instantiating and destroying gameobject is not a good technique for mobile platforms. If i am firing a bullet i should use pooling system.

Now I have many maps for the game.

How to manage this in unity?

I should create different different scenes for that or I should add maps in one scene and activate whichever is required or I should instantiate the required map at runtime or any other method?

Other optimizing techniques will also be helpful.

Try this Unite talk for a start: