00 - Before starting to coloring I clean the image in PhotoShop, I take away what I need unnecessary and redrawn if need be;
01 - I start the coloring with the base colors;
02 - I make the shadows, for skin and hair I use two colors to make the shadows because I think it looks more beautiful;
03 - I do the lighting and on the skin I make the white edges to have a better light effect;
04 - After the coloring of the character is finished I make the part of the background with the base color;
05 - Apply a texture in the background using two or three colors;
06 - I make the illumination of the bottom and also a border around the character to give featured;
07 - When everything is ready I go to PhotoShop and apply some filters;
08 - To finish the image I go back to Paint Tool Sai and do some more light effects.
Tutorial requested por @ macbethsama, I hope it helped you!