Ignore the book. But so that you know, what it is referring to is a short cut to an 18% grey card reading. Skin is lighter than 18% grey so if you increase exposure to compensate, by approx one stop, you will be about there.
Books seem to like complicating things and forget that you have an LCD with an image for reference, plus the all important histogram. Follow the histogram and you won't go wrong.
I use E-TTL all the time, on Av for fill flash. In this mode, the camera will meter for the ambient light, and also balance the flash exposure with it (but you may have to enable the right custom function so that the camera doesn't give a fixed shutter speed with flash - it's Custom Function 1-7 on my 40D).
This usually works fine, but you might not always like the result as sometimes the flash is set a little too bright - it's just a matter of taste. If you want the subject lighter or darker, adjust the flash exposure compensation on the gun. For the background, adjust the camera's exposure compensation which alters the ambient light level. It's a doddle.
You should also be aware of the FEL function (Flash Exposure Lock) especially when shooting people and you have framed the picture so that they are not in the centre. In this situation, because of the way flash illumination falls away very quickly over distance, there is a danger that the flash will try to expose for the background, resulting in over exposure of the subject. With Flash Exposure Lock, you frame the subject centrally, press the FEL button (it may be the * button on your camera, like it is on mine) and this fires the pre-flash and sets the flash exposure. When you reframe to take the picture, this exposure information is retained for the right result. Flash is very distance sensitive so if the subject moves, always do the FEL thing again. The handbook explains all this. Post again if you're not clear
Just to clarify how modern flash systems work, some people are not aware that there is a pre-flash as it is normally fired so quickly before the main flash that nobody notices it. It's essential for all automatic flash exposure control. You can see it through the viewfinder when you fire the flash normally in E-TTL mode, which when you think about it can only be the pre-flash as the main flash is invisible through the viewfinder - it's obviously blacked out by the mirror.
