To draw clearly defined lines on the surface of an object, one effective method would be to simply lay one or more 2D planes onto it's surface(s).
Add the first plane and -
Reduce it's thickness so it ends up as a very thin line.
Give it a material slot and colour it black, remove it's specular so it won't reflect light.
Add as many of these as you wish, (or duplicate the first) and drag them around as required
Once positioned correctly (a tad above the cube's surface), either parent or join them to the cube when animation is involved. (so they don't get left behind)
You could as an alternative subdivide the cube's surface to form the lines but that may introduce unnecessary complication at some point down the track. The planes on the other hand are independent and can be removed, reshaped, and changed about at will.