I use a mounted flash with diffuser and avoid shooting into people's faces. Still, it is very hard to get things right. I have to play around with the white balance settings for quite some time in order to get things right; by "right" I mean something to my liking and not what accurately reflects the skin tone of people. Is this a common problem?

Reading this got me a bit worried:

"If I take a picture outside without a flash, I'll look okay... I guess. But if I take a picture of me at night time with flash I look hideously ugly, like outrageously ugly. I can't take it. I'm afraid that's how I look like. I want to die. Why is this happening?"

https://uk.answers.yahoo.com/question/index?qid=20100617213903AATkRIN

Dom

[RKKS08]

I may add one point to the reasonable answers of your link:

A rule of thumb would be that person will look (n) years older than it is, where n >= 2*(hours since getting off from sleep).
Women know what to do about this, and making cosmetic industry earning billions.

This rule may not apply to very young people.

[aleonx3]

It is all about lighting and it is up to the photographer to do it right (flash or no flash).

[maxfield_photo]

Very few photographers take the time to gel their flash to match the ambient light. I'm as guilty as the next person, but it really does help. The mismatch of light sources is extremely disconcerting to the human brain, and that's because we are born with such good built-in "auto white balance" systems. If there has to be a mismatch, you normally want the warmer light source falling on the subject and the ambient light as the cooler color. Unfortunately, when shooting under tungsten lighting with an un-gelled flash, the opposite is what you get - cool subject and warm background; it looks terrible.

The natural color temperature of the flash is usually about 5500 Kelvin, but I know a few professional photographers who always set their white balance to 6000 Kelvin when using an un-gelled flash. It gives people that golden glow. Even when they gel their flashes, they still keep the WB about 500 degrees warmer than what the flash is actually putting out. So if the add a full cut CTO to bring the flash to 2800 K, the set their camera for 3300 K.

[carrrlangas]

take the time to gel their flash to match the ambient light.

+1 on this. Makes a huge difference. Even if it´s just a little correction. I think you are on the right track getting the best white balance first, the gels should help. Also, you can play with saturation and luminance of red, orange and yellows to get better tone. and if you are getting too much specular highlights it´s because the light from the strobe is reflecting into your lens. Try a greater angle between lens axis and strobe and / or a longer lens. You could also try a color chart to get a better profile and a grey card to get very accurate exposure.