One of the most freeing and fun steps for me is applying the underpainting. You can’t really make a mistake here. Start with prayer, and then begin to apply the paint. What you are doing is doing is establishing the dark, neutral undercolors that will provide the shadows and darker areas for the icon. In a way, this is the “ugly” stage of the icon.
Once the undertones are established, most of the modelling and definition of the features will be done through the painting of the light. I have always liked that analogy of the light creating shape and form out of darkness, spiritually as well as artistically!
It can take a long time to build up the highlights using transparent light colors on top of a dark ground. Patience is required, but sooner or later, patience is rewarded with a soft, glowing highlight.
I make many mistakes along the way, but with a long slow process such as this, they can easily be painted over. Whether it is wrong color in the background (yes, that is happening here for sure), an uneven texture (that, too), or a minor drawing correction (probably), it is fairly easy to correct. Many careful and wise iconographers make color and highlight studies beforehand, but impatient ones like me prefer to work out the problems right on the board, and to experiment freely all the while.