the majority of your dice roll determines the result.
So if you're going to a new tile, and it's surrounded by 3 forests and a desert. Then you would set aside a dice with a 2 set. And then roll the remaining 2 dice. This should make the odds more likely to roll another forest.
This should make the map look a little more normal and less sporadic with a bunch of different terrains.
The dice do what they want. But statistically it should help make the map a little prettier.