Hi Troppo, first of all, ideally you need a paint that's erasable, you also should work in light coats of paint so that there isn't much paint to erase.
There isn't much to erasing to be honest but its wickedly effective, giving great effects.
I use several things to erase. I have an electric eraser which I use for harsh highlights like the eye highlight, it also is good for skin texture, you have to sort of dab it on the painting as if you we're doing dots. It can be used for lines too. I use fine scotchbrite for skin texture and also to lighten areas in general.
Pencil erasers are good because you can sharpen them you can do fine highlights, and because they are double ended you have a hard and soft option. Normal erasers are also good to use, any type, just try it and see how it erases.
I also use a rounded scalpel blade for skin textures and wrinkles, it can be used to do anything though not just skin. I use it a lot.
Basically anything that can rub your paint out you can use to erase.
I hope that this helps a little.