How do you get from the photo stage to the drawing stage? Well, if its a western style pen and ink illustration, it usually means doing an underdrawing to use as a guide for the final ink drawing. This I like to do directly onto the board that I will use for the final drawing, and not a pre-sketch on a separate piece of paper.
What kind of surface should this be? Well I like to use either Bristol Board in a pad, it has a very smooth surface that allows technical drawing pen nibs to glide across the surface without skipping, and it keeps the line nice and tight, with no bleeding at all. It also takes washes well if you are so inclined. I also use Caslon Bristol Fine Art Board for larger pictures, it has the very best surface and can even be scraped back to tidy up errors. Both have very white surfaces which is also important to me.
Beginning the initial Sketch. I begin with the sketch, which I actually do using a light blue pencil (a polymer lead in a technical pencil at about .5mm - the type that used to be used for drawing paste up lines for artwork). This pencil doesnt show up when artwork is scanned (if you forget and leave some) and also when you are inking over you can see what you still have to be done. I try to be fairly free with the line, and don't use a ruler as much as I used to, but I have had a lot of practice at drawing straight lines freehand. It doesn't hurt to use a ruler to draw a line in blue, you can draw freeehand over the top using the pen later to give a lighter feel.
Alterations. It is easy at this stage to rub things out with a plastic rubber if you havent drawn too hard with the pencil. Please be careful at this stage to go lightly with the paper, if you stain it you might have to start again. Bristol Board can easily withstand erasing a line several times before the surface breaks down. And line board is even tougher, but you still have to take care.
Drawing. I use the photos as a guide, I dont trace or anything, although sometimes I measure lines with a ruler. Your picture is an impression of the scene, not a photo (you have that already). You can change things, leave things out etc. You are the artist and it is your picture (until you sell it). I try at this stage to work out what areas are going to be the lightest and what are going to be the darkest. I shade using the blue pencil, in preparation for hatching which will be done with the pen. Don't shade too dark or it is difficult to erase later on. Continue until you have rendered the whole scene that you want to draw. I finish the whole picture in pencil before I move to the ink stage. You should at this point have a cool blue picture that you are happy with before we move to the best bit - drawing the final picture using ink. This is the bit where the picture comes alive!