Terrain best practices

Hello,

I’m a beginner with Unity. I have read some tutorials about the terrain editor. I understand how to do a terrain, but I need your advices about optimization.

Is there good practices (best practices) to set terrain in order to be used on pc game and tablet ?
I cannot understand why on some samples terrain has a low draw call on stat windows and mine is very higher).
Thanks for your help.

http://wiki.unity3d.com/index.php/Terrain_tutorial

A bit old but still a great place to start.