If you meant smoothness in shading/blending, I started out just doing monochrome portraits for a long time, so just focusing on toning with one colour, before I moved on to colours and added just 2 or maximum 3 different colours.
For colouring hair with colour pencils, I work in segments, drawing strand by strand in detail by adding darker shadows and leaving highlighted areas uncoloured. For digital hair colouring, I work in layers, laying in darker colours first, before gradually using smaller brushes for highlights and shadows. When in doubt, there's always youtube for tutorials!