What is the best position of the troops when I make a formation?

This may depend on who or what you are attacking and the troops / heroes you have available. But the general idea is to have a strong defence at the front and the troops with the best range attack at the back. Fighters in row 1, vehicles in row 2 and shooters in row 3. But if you only have 2 heroes for example and they work best with other troops then just look for the combination that gives you the best combat power rating.