Oh, I think I can do something on this one! Just wait.
Edit:
So, this is actually something I first tried out a couple of months ago. So far I think it has been a great help. Some of you may remember the stuff I posted in the Merry Doodles thread a while back.
http://i254.photobucket.com/albums/hh107/GD_/Muut%20harjoitukset/construction-1.jpghttp://i254.photobucket.com/albums/hh107/GD_/Muut%20harjoitukset/construction2.jpgAnyhow, this is basically what MetallicDragon was saying. You need to see the basic 3D forms to understand what you're drawing and to do it correctly. Some knowledge of perspective will come in handy, too, especially if you ever want to draw stuff from your head.
1: You can paste the photo in the same image you're going to draw in for easy reference. You could make it smaller or bigger than the drawing you're going to make to raise difficulty.
2: This is what I see as the basic shape of Dalek. A rounded cone.
3: Here you can see the shape from different directions. You should be able to do this part in your head to make sure you really know what the object looks like in 3D. This applies to all the other shapes you are going to add as well. It would take too long to actually draw all the different positions, so you just have to rely on your imagination. Note that this part is especially important if you don't have a photo for reference, and if you want to draw the thing from different agles than shown in the photo.
4: You should start by adding the biggest and most obvious parts. I decided to add the ring first, because it's the most noticeable part.
5: Here's another ring of some sort.
6: I defined the top part more to show that it's pretty much the half of a sphere attached to a cylinder. This is also where you see all the most basic shapes in the Dalek. Notice how perspective affects the circles going through the object. The further away they are are from their vanishing point, the rounder they appear. The circle at the top is a bit wrong in regards to that, but I was just lazy, so pay no attention to it.
7: I cleaned out everything you can't actually see from this angle, because it's about time to start adding the surface details. Trust me, you don't want to draw all the details on the opposite side, too.
8: Two more rings and some plates around the Dalek.
9: Some more details. The curvy lines in the middle are to help with positioning the lamps. See how these are also affected by perspective.
10: The final steps of the sketch are done, so after this you could check it for mistakes, redefine the outlines and start coloring, if you will.
In case you were wondering about the vanishing point and perspective, I decided to define those, too. Assuming that the two circled parts are pretty much level to horizon and both are facing the same direction, you can define the vanishing point by striking two lines through them and seeing where they meet. You can draw the horizon line on that point.
I hope this helps somewhat. Just remember to think in the basic shapes, like cubes, cones, cylinders and spheres.
