When not busy sleeping or whining about flight nurses and paramedics, most EMS pilots spend a lot of time looking at maps and preplanning as many flights as possible until they become very familiar with their area of operations.
Throw in GPS and other navaids and it gets a lot easier. Setting the cockpit up as if it were an IFR flight helps as well should the weather deteriorate.
I find marking my map in "miles to run" to the destination and using the GPS to "count down" the distance makes putting a finger on your location much easier.
One could always use the home base as the waypoint and then "count up" along the bearing shown by the GPS.
Most EMS bases have a big wall map with a string and protractor that allows a pilot to quickly plot a direction and distance to the scene....or for frequently used sites, a gouge sheet with all the information for the trip.