You can build near your Reincarnation Site or near a built building of your tribe. You can not build:

 

- On water

 

- Too close to water (shore)

 

- Too close to a building

 

- On irregular terrains (too step, etc)

 

- Too close to some objects (stone heads, prison, reincarnation pilars, etc)

 

 

It is important to see how many trees you have avaliable, so you know weather you shoud build freely above them, or if you should avoid trying to place plans on them. 

Also, it's risky to build too close to the enemy settlement.

If you have the option to start a second settlement somewhere, it is also recomendable to. This way, your base will be split, and you will have more ways to atack from.

 

So, now you understand the concept behind building, but generally you will want to build everywhere possible, making sure you waste the less room you can, so more buildings will fit. Also, build importanter buildings - like training huts - in the back or your settlement, or somewhere well protected, where your enemy will have a hard time to reach.