Firstly I would HIGHLY recommend using an image you're familiar with. Doesn't necessarily have to be the easiest one just one you personally enjoy and are familiar with. If you've previously coloured one in photograph it then use your photo editting software and turn it into GREYSCALE. A lot of the free programs also do this.
This will be your guide whilst you train your brain to think in monotone. So firstly grab your coloured image, I've used Miss Mirabelle by Hannah Lynn (Crafts & Me)
OK feeling confident? Grab a full set of greys - I use COOL GREY 1-5 plus the BLENDER. If you think in terms of skin tones then the blender will be equivalent of ivory, cool grey 1 will be your blush and cool grey 2 your vanilla or colour you use for shadow.
For the skin tone I started with the darkest colour first in the shadow areas on the skin so use COOL GREY 2 and add some shading.
Next use your COOL GREY 1 which will be the equivalent of your blush and working from the dark into the light blend the colours in
Then to finish the skin off use your blender which is the same as ivory and it should be looking nice and luminous like below :)
Next look at your greyscale image and you'll see the bra bit is darker than the top so I used the darkest greys here COOL GREY 4 & 5 and a lighter mix for the top COOL GREY 3 & 4. If anything appears to dark just run your blender over it lightly and let it dry.
Then onto the hair, I used COOL GREY 5 for the darkest parts at the roots etc then blend that in with a mid tone COOL GREY 3 then the lightest bits are COOL GREY 1. You can also leave a bit of white showing or again use the blender to lighten the highlight points.
And here she is completed! I only did one layer on this one but you can add a bit more depth to it doing a 2nd layer or using coloursoft/prisma pencil too
Here's the 2 completed side by side. Hope you enjoyed the tutorial and do have a go at this lovely technique, you'll be hooked!