What a beautiful medium this is, it can be a very slow and tiring process painting a decent size picture using pencils, having to add layers and in particular the blending of two or more colours, but the end results are usually stunning. I use Faber Castell polychromos alongside of Prismacolour Premier pencils, both are excellent but very different in application.
The F.C are hard wax based and thereby hold a point for longer, whereas the P.P are very soft, being smooth and thick and easily blended with great coverage, and can be layered over the top of the F.C
I have the Sets of 150 of each brand, and while this is overkill most of the time, it is good to have a choice of colour to use instead of the usual limted few.
Most of the pictures you will make dont usually use more than approx 10-12 colours in total, but what you can achieve just using these is immense. Being softer, the P.P pencils dont hold a point for too long, so if you watch a youtube video on using them, you may see user twisting the pencil quite often, this is too keep the point on the pencil as long as possible.
The pattern for this picture came from a brilliant artist by the name of Marian Jackson, MDA, you can find lots of patterns and tutorials on her site , give it a go..