Longitude and Latitude
Typically you should choose a longitude and latitude and render it at a reasonably distant position. Once you're happy with the position start reducing the range or the camera aperture.
The radius of Mars is on average 3396 km. To get the whole planet in shot (camera aperture is 60 degrees) choose a range of around 10,000 km. The minimum range is set to avoid accidentally being positioned inside the planet and to avoid seeing data artifacts. The resolution of the surface is at worst a 1.8 km grid at the equator.Height scale
For an undistorted topology rendering choose a height scale of 1. For more dramatic effects increase the scaling. Normally the amount of scaling required reduces as the range decreases. Note the cloud height is also scaled by this amount.