The app uses HERE so you're going to get the best navigation results on the app if you plan using HERE a well.
If you use other devices, be sure to plan using their base router, i.e. TomTom or Garmin (= HERE).
And if you're trying to satisfy a whole group of disparate users, then definitely buy the Gold subscription and use the Toolkit -> 'Compare route with' function in the Route Lab. You'll be amazed/surprised/horrified at the differences, but adding extra waypoints can pull them all in to match.
Lastly, on the GPS front, calibrate your phone. A Google search will tell you how.