This tip is a quick one. Isometric maps are fun, and can have a large impact. The side on view gives the option for more detail and a more illustrative style.
Rivers can break or make an isometric map. On a top down map, a rivers travel in all directions. On an isometric map they should travel further left to right, than up and down. If a river travels straight up and down on an isometric map it’ll look out of place. In the map above I’ve pulled the curves of the rivers further out when they travel left and right. This helps sell the idea that you’re looking down on the map from an angle. This, combined with the same trick on the coasts, can sell the perspective and foreshortening that the isometric map requires.