The Bali Domestic Terminal is not too difficult to find once you have found your way to the Ngurah Rai International Airport. It's located on the ground level of the building.
Following the pictures I've taken below will show you how to get there after entering through the main entrance of the airport. The Bali airport is a new building that has only been operating since the first half of 2013. The pictures below are as of November 2013.
After walking through the main entrance to the Ngurah Rai International Airport, I eventually saw this cafe and in front are some lifts that takes you up to the third level where the international terminal is located.
All you have to do is keep walking straight and you will eventually come across this cafe. It's located on the far left hand side of the airport on the ground level.
I was standing in pretty much the same position as the above picture when I took this one below. I am facing left from the picture above and this is the direction to go to find the Bali domestic terminal. Once you find the cafe and lifts pictured above, the terminal is close by just around the corner basically.
After walking down towards the end of the airport from the picture above, it will take you to this corridor here which is where you have to go to get to the departure gates for all domestic air travel in Indonesia. There are some signs showing where the terminal is located once you have reached this point.
Part of the way down the corridor towards the domestic terminal you will find some ticketing windows. From here you can purchase airline tickets and find any other general information that you may need.
After progressing further down the corridor you will come to this point here. This is the main entry point to all the departure gates for domestic flights in Indonesia. I wasn't able to take any more pictures after this point as I would need a boarding pass to go through.
I took this picture after turning around facing the other direction from the picture above. At the end of the corridor is back to the area shown in the first 2 pictures on this page.
The domestic terminal is still under construction along with other areas of the Ngurah Rai International Airport. The old Bali airport was operational earlier in 2013 so this building is very new. As the airport is still new, I expect to see further developments in the near future.