There are a lot of clues that you can use to determine the contents of a stack. Early on you can guess the contents of a stack by how many times it has split. If you happen to remember the die rolls, you can usually determine what is in a stack. When a stack capable of recruiting moves into a terrain and doesn't recruit it probably means that the stack does not have any natives. In the late game, you can figure out how many top-level creatures your opponent has by subtracting the number still available and the number killed from 10.
When in doubt assume that the strongest creatures are in an enemy stack. This lessens the change that you will move your legion into an unsafe position and lose it.
ran cyc - recruits in marsh, plains, brush, and jungle. Will
quickly become a big stack.
ran gar - same as above.
cyc cyc cyc from beh gor gar gar. Both stacks recruit behemoths in
the jungle and gorgons in the brush. Soon you should have two
big stacks, because nobody wants to fight burly green creatures in
the bramble.
When you attack with overwhelming forces, your opponent usually flees and you only get half points. However, when your opponent has some chance of winning, many times he will fight and you will get full points. There will be a small chance that you will lose, but it only takes a handful of marginal victories before you get teleport.