INTRODUCTION:
Noses come in all shapes, sizes and colours. In my opinion, the fundamental skills to learn as an artist is perspective, lighting and shading... almost anything can look good with great lighting and shading ;)

I normally do most of my painting on a single layer. Don’t get discouraged in the initial stages when it looks rough, it only matters what it looks like when you’ve finished :)

There is no ‘right’ or ‘wrong’ way to go about it. Have a look at other artists techniques and adopt one or adapt to suit yourself, it all comes with practice.

I pretty much use a single brush in Photoshop, just the soft round brush, but vary the size and pressure using a Wacom. This painting however, I started experimenting with a ‘splatter’ brush to give a little texture, which is required especially when painting men or the elderly.
Start off with basic sketch, then change the layer blending mode to ‘Multiply’. Create a new layer as your painting layer under the sketch layer. Start adding basic colour.
Keep working with basic shades, keeping in mind where the light source/s are. Add more detail as you go.
Using the splatter brush, with the spacing increased in the brush properties (in the brush panel), start adding some lighter tones. The spacing with create a ‘dabbing’ effect when you apply the brush but be mindful you need it to look random. Takes a bit of practice and patience ;) 
Turn the sketch layer off, then start adding shadow. As we are going for ‘Realism’, objects don’t have outlines in real life, so we add shadow and highlight, NOT outline.
Keep working with highlights and shadows to build up the image and consequently adding the appearance of depth. Finally, add a few specular highlights with both the regular and splatter brush. Boom!
Finished Painting