The general question is, what style do you want - more a 'map' style or more of a 'aerial image' many fantasy maps are somewhere in between. Often they seem to detailed for a pure map and the same time to simplified to be 'real'.

So tips depend on which direction you want to go. If you are looking for the more 'realistic' map, one idea might be different shadows which correspond to the height of the buildings. Towers have longer shadows than walls, two story buildings higher shadows than huts.
And the classic 'drop shadow' has one problem, it is not the shadow of a three dimensional object, but of a hovering plane...