Use softer blacks
How to use it
Use a dark grey instead of black throughout your interface.
When to use it
Flat blacks - with a brightness value of 0 - look quite unnatural, because we never see flat blacks in nature. Black things usually reflect some light, so they're actually a dark grey. Lower contrast values, like you'd get between light grey and dark grey, can be easier on the eyes than pure white and pure black.
Most users won't realise that the dark grey is not a black, but the interface will look better.
What to watch out for
You don't need to soften the black a lot to get the right effect.