>>96306450
you want hills, towers and other significant line of sight blocking elements, also low walls
and you want all of that in the middle of the board, away from deployment zones
you don't want to make the deployment zones comfortable and the middle of the board without shit to move around or hide behind

rivers look cool, but ruin games unless they're effectively irrelevant
the most practical hills come in 2 forms: a) "it's actually a temple" and b) "gentle slope on one side, drastic cliff on the other"