I find a good way to keep track of the whole image, as well as balance things out is to use a grid of thirds, something I've discussed before. You can see here, especially with another 5 minutes worth of progress, that each quadrant is used for a slightly different thing. The top left has a mixture of cliffs, open sky, and some roughly sketched in haze/cloud detail. The top middle has the vertical sky beams, as well as the distant rock features, while the top right has a mix of foreground cliffs and sky, the sky showing through some of the cliff to show an interesting silhouette. The middle left third has cliffs that frame the main structure, while the very middle third has the main structure in one corner, balanced by a vague city (now made brighter) that sits right on the middle of the junction of thirds. The right middle quadrant has cliffs, which in this third I tried to add some slight lateral detail to. The bottom left is mostly framed in by foreground cliffs, complemented by a curve in the road, the bottom middle is all road, with all the angles they bring, and the bottom right is almost entirely vertical cliff.
The new sections added to the main structure are mostly introducing some more contrast, to help it stand out and be more visually interesting. The large angled support stands out among the many vertical and horizontal lines, and the two new "waterfalls" and the divisions in the wide "window" add what I like to think of as "contrast of density". This effectively means that this comparatively large amount of detail will make the object be more visible compared to the less detailed areas around it. I discussed in a post about contrast, our eyes are drawn to things that stand out from their surroundings, and this is a fairly interesting way of achieving this.
If you compare the city and the roadway to the previous version of the image, you can see I added much more contrast here, too, with brighter values really helping these to stand out in the composition. This really helps highlight the s-curve, which I want to feature fairly strongly, and also helps balance the image, which was previously a little more focused on the left hand side. I also tried to made the framing a little more interesting around the city, with the cliff now jutting out slightly, to "catch" the city, rather than the cliffs running all the way downwards past it.
The other adjustment here is that I tried to start filling in this patch of blank sky. I used very quick, messy strokes to scratch in my ideas for a loose gradient of colours, from the glow shown at the very bottom of the main structure all the way up to the sky colour. This ends up being a sort of hazy, cloudy kind of detail that doesn't mind being a little messy, and fills up some of this dull, flat sky with some visual noise that's not too distracting, but not dull and flat either.
And that, with a little more fiddling with some of the rocky features, is the end of the second 5 minute snapshot of this speedpainting. The differences between this and the last mostly represent me focusing on getting a composition I like, and making sure each section of the image is fairly well balanced, and works with the rest. With this basic composition at a level I'm roughly satisfied with, my next step was to start thinking about colour, which is what I'll be looking at tomorrow!