[Quiet Man Cometh]

I agree with Poggio on the type of pencil crayon thing. The cheaper coloured pencils tend to have a higher wax content and they don't blend or layer as well. Prismacolours are my favourite but Staedtler isn't that bad for the cheaper sets.

In art class the main thing my teacher told is, which I will say now, is to use a very soft touch, because if you have a sharp edge on your pencil crayon and end up making a hard, solid line, you will never be able to get rid of it. This mean lots and lots of building up colours and layers rather than starting out with hard colours.

Practice different pressures to get the different shades from one pencil, which is sounds like you already do. You can mix and blend colours directly on a drawing. Blending colours is easy if you use a light touch and don't press too hard to start with. Just colour overtop of another colour to mix them.

Also, pencil crayon, I find, will only layer so much before colour just stops transferring onto the paper. As an example of paper, I've found that plain old smooth printer paper makes for nice and easy blending, but doesn't take as many layers.

And just to mention, my general experience is that pencil crayon art does not scan well.