Today I wish to give an insight of what I do before start copying a picture, or making a drawing. There is much of what I read in books and blogs, and I hope you will find something useful for your own drawings.
(Note: I drafted this post before Carol wrote hers: How to plan a drawing – well worth reading!)
I usually start with a picture I found particularly beautiful:

I chose it because I like horses very much, and also because it is already in black and white, so that I can copy it with a single, simple pencil. The picture come from the blog FantastykVoyage.
What I do first is to follow slowly with my eyes all the borders in the picture. I start with the most obvious and sharp – eyes, eyelids, nostrils, cheeks. These borders are the lines that you would draw if you made a comic or a very quick sketch.

Then I try to find other borders, this time between different areas with the same shade. For example the black shadow of the nostril, the shadows of blood vessels, the different shines of the coat on the head. Try to forget that it is the picture of a horse. Focus only on the shapes. This first scan through the picture will help you later, when you will actually draw – you will remember the lines you observed.
A useful step is now to check proportions and establish a (mental) grid. Divide the picture with crosshairs or a finer grid. You can actually do it by superimposing a transparent sheet and draw the crosshairs with a felt pen; you can print the picture and draw the crosshairs directly over it. Don’t worry if you scribble on the printout, if it helps you get a better drawing as a result! This step will help you judging relative proportions of the shapes you will draw, and where they cross the grid or the borders of the picture.

Sometimes I start drawing at this point: I draw all these borders, the ones from the subject itself and the ones from the shades. Sometimes I don’t, and wait for next observation step. Sometimes I grab a camera and take a picture, sometimes I don’t do anything at all, I am just happy to have found a great subject to observe.
Next step is observing which areas have the same shade. It is useful to have scanned the picture as a whole before starting with the actual drawing, because I find much harder to start shading the first area in my drawing and then have to calibrate all further fills one at a time – it makes much more sense for me to draw all borders (some only very lightly) and then fill all areas with the same shade in one go, then pick the next shade and fill all its areas. Imagine to paint one colour at a time. You can be helped by image editing software, that has tools for the selection of areas with same colour.
I had made an experiment with GIMP 2.8 and Posterize tool, that flattens the image to a given number of colours. In the case of a black and white picture, it uses black, white, and different greys. See Yalla’s picture with 2, 3, 4 and 5 levels. Nice observation exercise: find all areas with the same colour. It gets quite hard with over 5 levels but I assure it is rewarding and useful.
2 levels: black and white
3 levels: black, white, grey
4 levels
5 levels
You can decide to start with the darker areas or the lighter, as you wish; if you don’t know yet, try both approaches.
Now choose a tool and a technique and start drawing: pencil, fine-pointed pen, charcoal, watercolour; lines, meshes, uniform shades, points… and have a great time drawing!