My Apple Watch battery life is 12 hours. Is that normal? What can I do to improve it ?

There are some useful tips here:

Batteries - Maximizing Performance - Apple

Click on the watch at the top to skip all the iPhone, iPad stuff.

My watch usually lasts all day even with exercise, but time is shortened if I use maps live, etc.

Battery life varies by use, configuration, cellular network, signal strength, and many other factors; actual results will vary.