Secrets ?there are none!
There are no secrets about figure painting.It is mostly practice,practice,practice.
Like a friend of mine said,that is why he married a teacher,they make you do it over and over again until you get it right.
But seriously,to be successful using my method ,you must use my method.Not sorta use it ,use this but not that or cheat a little here and there.If you commit to this ,I can guarantee good results,if not don't even bother reading any further.I know this sounds harsh but it is born out of frustration ,as I have been asked in the past over and over "how do you paint figures ?"and when I explain what is required it is clear to me that no one really is listening.
First and foremost ,save the paint that you have been painting with up until now for your cars ,airplanes or whatever, but don't let it even near your figures.
Go out and buy FLAT acrylic gouache paint.There are only 2 brands that I am aware of, JoSonja by Chroma or Acrylicos Vallejo (and no I don't have shares in either company nor have I ever even received a free tube of paint from any of them.)All of my experience has been with using the JoSonja brand ,so that is what I recommend you buy because there may be differences between the 2 brands that I am not aware of .
For those who know how to mix paints buy the primary colors,for those who don't ,try to stick with the tube colors.Why? because unless you mix twice as much as you need and save it ,you will have one hell of a time getting back to your original color. Acrylics also have this nasty habit of drying to a darker shade.
No matter what the hobby or art store guy tells you there are NO substitutes.Your success as a figure painter ,using my method ,depends upon using flat paint,period.
While you are in the art store ,you may want to pick up some Gesso.It comes in various colors usually black,white,burnt umber and gray.Be careful using white gesso because if it chips or somehow contaminates the surface that you are working on ,those damn little white specks will go everywhere that you don't want them to go.You can use white or any of the other colored gesso as a substitute for the tube paint ,as it will also dry absolutely flat.
Why all this emphasis on flat paint ? because future shading will be done will chalk pastels and chalk pastels will not stick to paint that has varnish in it!
Areas that require some shine to it like leather ,can be buffed with your bare finger prior to shading.The skin of your finger can be used as a very fine abrasive and facial oil from your nose looks great on leather.(well maybe there are a few secrets after all!)