Mostly I make realistic looking characters, sometimes semi-realistic. So I tend to go for neutral colours like browns, blacks, whites and greys, occasionally throwing something a bit brighter in there just to add a bit of colour, like green or red. With some characters, mostly the semi-realistic ones, I add markings or colours that help to reflect their personalities or background. But the colours have to go well together. I hate it when people have a mixture of colours that clash, like bright blue and red. That hurts my eyes. >.<
I can spend ages reviewing a characters appearance, tweaking the colours or dimensions, if I notice that something isn't quite perfect or I change my mind about something. I remember spending about an hour making a character and going back and changing things before I thought it was ready to be seen by everyone. XD
Generally, I'd use a photo as reference for the basics of my character like body shape, muzzle length, ear shape and typical colouration.
One thing I avoid doing is if part of my character is black, I don't make it so the RGB sliders are all on 0. I'll put them on 5 so that it looks really black but the fur texture is still visible.