The first thing I was concerned with was the creature design and the colossal scale it had to convey. To do this some good results can generally be achieved by adding a scale reference. For example, it could be a person, doors/windows, birds flying etc. Because we know how big all those things are, when we put them next to our subjects it gives a sense of scale that would otherwise be difficult to convey.
The use of perspective with a really zoomed out field of view or a fisheye lens effect also affects perception of scale. Another very helpful thing is cutting something off the frame. The viewer will perceive a subject to be huge if it cannot even fit into the picture; it implies there’s so much out there and leaves something to the imagination, which is generally a pleasing effect anyway. In this case you can only the pretty big head so we assume the full body must be enormous.
After a quick exploration on paper I moved to Photoshop for this sketch. Most important problems are solved at this stage: composition, rough perspective, patterns of light and darks, big shapes vs. details and so on. I generally leave the color to a later stage (Fig.02).