Drawing lightly with a pencil, create a simple framework of circles and lines.
Using the framework as a guide, you can now begin to flesh out Grievous' body. Start by giving him an upper "teardrop" shape and then use angular shapes to show where his shoulder plates are, forearms, legs, etc.
Outline the areas where his torso, legs and feet are. At this stage, make sure your illustration is still just light pencil lines, and then later you can fill in these dark areas with marker. For now, just focus on getting the shapes right. If something looks strange to you, go ahead and erase your pencil lines and try it again.
Time to start adding in some details, as well as Grievous' collar section and the basic outline of his head.
Focus on getting his head shape exactly how you want it. Start with the eyes and then work your way out. Remember to make him look menacing. Grievous is almost always in a bad mood and ready to take down some Jedi. When it comes to drawing this Droid General, the meaner he looks, the better!
At this point, you should have a fairly detailed pencil drawing. Add in any final details that you may have missed, or adjust anything that looks out of place. Once you're happy with how your masterpiece looks, you can go over your lines with pen, marker, or heavier pencil line.
You can color your drawing, too, if you prefer. It's completely up to you!