depends on what you are using.
If you are trying for the water color look on a computer I'm likely to be of very little help.
But if you are using brushes and pigments on paper then there I might be able to make some suggestions. As that is my favored media for map making.
There is just something cool about tactile maps.
The detail in experimenting with pigments and artificial aging, the folding and creasing if theye are desires. The staining and disintegrating corners.
The hand work in getting the details and the occasional happy accident.
Sorry I get a little carried away