What to Tackle First?
When attempting to rescue an otherwise promising image unfortunately plagued with multiple problems it can sometimes be difficult to know what to tackle first. Recommendations have evolved over the years in response to changing technology.
In some senses, digital image editing has been around since computers were first capable of displaying images. But the birth of serious image editing is generally traced to the introduction of Adobe Photoshop well over 20 years ago now. Editing capabilities back then were understandably primitive by today's standards but it's worth considering the basic approach as a basis for what came after. Images even then were stored as arrays of pixels, each of which had an associated color value. Notably though, that's all images were back then. If you edited an image, you changed the color of one or more images, replacing their former value with a new one. Images had no history, and each change had no direct influence on any other change. If you changed a pixel to a certain shade of red it really didn't matter what color it used to be or how many other colors it had been before that. In this sense, to the extent that people even talked about digital image editing, nobody really talked about what order to apply changes when doing so.
As the tools for editing became more sophisticated, it was only natural that they got used more. Users got more demanding of what they expected, and they therefore obsessed more over each image, using every tool possible as often as possible. Competition between users for new and clever ways to use the available tools also ensued with the resultant further ratcheting up editing tweaks. All this editing took its toll on image quality with a notable loss of detail, and therefore a notable increase of frustration among photographers.
The cause was clear. The world of digital is the world of zeroes and ones. Fractions get lost, and each time they do they take some of the image detail with them. Given this, users started thinking about how to avoid damaging their images by optimally ordering their editing steps.
Over the years since, various editing enhancements have been added including layers, masks, channels, and transparency. Each of these has had an impact on how best to achieve a desired result, and thus an effect on what order to make the changes needed to reach that result. As soon as it became possible to create layers in Photoshop, photographers began to notice the ways in which they could interact with each other. You got a different result depending on which layer ended up on top of the other.
For both of the above reasons, it was common wisdom that global changes should be made before localized changes. But photographers don't all shoot the same subject matter either, and not every image starts out the same nor has the same needs. As such, opinions and approaches differed. Some users became quite dogmatic, proscribing a set sequence of steps not to be deviated from. The precise sequence differed somewhat, and such users often debated such topics, but the reasoning behind these competing approaches always came down to the same thing. The intent was always to streamline the steps to maximize efficiency while minimizing image degradation from repeated edits. Over time, as aspiring users gained editing skills themselves, they developed their own approach and steps.
Non-destructive editing techniques, generally involving adjustment layers or smart objects, helped too. By programmatically collapsing numerous editing steps, fewer actual pixel value changes took place, and image degradation was minimized. A Photoshop user could tweak an adjustment layer as many times as needed and only the final one ever actually got applied, and when it did, the changes from all other adjustment layers got applied with it.
The Develop module settings in Lightroom take all of the advances introduced in Photoshop even further. Even recent versions of Photoshop made things harder than need be since non-destructive edits often competed with traditional layer-based edits. Non-destructive adjustment layers could only be combined down to the first traditional layer underneath them. The process of rendering a composite image was therefore constrained into a step-wise application of calculations in groups dictated by competing layer types. While users could re-arrange the order of stacked layers to allow for combining more adjustment layers, doing so generally changed image appearance by altering what each layer thereby affected.
In Adobe Lightroom, there is no Layers panel. As such, no matter what order you do things in, the order in which those changes are actually applied is controlled by the software not the photographer. And of course everything in Lightroom is non-destructive so the program can more easily combine calculations resulting from a series of changes. The net result is that the order of user edits no longer has any real impact on image quality. Assuming you end up in the same place, it no longer really matters how you get there. This means Lightroom users are free to tackle whatever they feel they need to first without feeling a need to follow proscribed rules.
Personally, I generally start with the Spot Removal brush to get rid of distracting dust spots and other issues that get in my way of really evaluating an image. Then I can work on whatever strikes me first, be it the overall while balance or exposure, or more localized tweaks with the Graduated or Radial filters. Editing in Lightroom means you can do whatever seems to make sense with any given image and circumstance. Whatever works for you is fine since the images you are working on are yours.
But one issue of what to tackle first hasn't changed in the least and likely never will. No matter what you do in Photoshop, Lightroom or any other program can compensate fully for mistakes made in-camera. Information missing or degraded due to poor camera exposure or other mistakes in the field can never be fully restored. So the bottom line as to what to tackle first is to get as much right as you can in-camera. Digital photography is, after all, still photography.