I'm writing this at the office between patients and hope to add some illustrations later, but here's some general concepts about improving the image and I believe they apply regardless of the editing programme that you use.
Let's assume that in the raw software (Camera Raw in my case) I have optimized the image parameters. I should point out that this does not mean making the image look as nice as possible. On the contrary, my main function in setting the raw parameters is to make sure that all the information I need is in the output file. Quite often this means a muddy dark print in order to save highlights.
OK, the image is in Photoshop and I'm looking at it. the first thing to do is an overall correction. I want to pin the two ends of the image, black and white points without exceding them. At this point I'd rather miss reaching white and black by a little rather than risk losing data. I adjust the curve to produce the best possible overall image. I do this by deciding on overall brightness of the image, brightness of highlights and depth of the shadows.
A particularly flat image will need an S bend curve to increase contrast and shift pixels away from the middle thus increasing contrast. An image with overly bright highlights will need a sharp drop in the curve from pure white but will then need to straighten out quite quickly or else risk being overall too dark. An image that is overall too contrasty will need near vertical lines near the black point and white point with a fairly flat midsection. Of course I actually adjust the curve to suit the image, not to any preconceived ideas of what it might need. Curves can be quite complex with several dips or bumps to tame the overall image.
As you probably know from previous articles, I do most of the rest of the adjustments with curves and black masks, painting light into the masks to apply the curves to specific areas of the image and in amounts to suit. That's fine but what I would like to try to discuss is what I'm trying to achieve by doing so - it's all very well saying that the areas that are too dark need lightening and visa versa but how do I know they are too dark. What if they really should be darker. As the late Fred Picker used to day - 'let the tones go the direction they want to go' - instead of dodging shadows, burn them in so they are nice and deep - of course that presumed a perfectly exposed and developed negative in the first place, not a rescue job on a negative you wouldn't wish on your worst enemy - funny how many of those we seem to have in our files.
OK, so how can I discuss general rules of tonality? Let's take one of my badlands images shot after sunset (and therefore in fairly flat light). Contrast containment is not a problem. I try increasing the overall contrast to give the image some snap but note that it now looks harsh. I'm going to have to be more selective. As the image is rather flat looking I do increase contrast a little but it still looks two dimensional even though contrast is now better. What I'd like to do is make it look more three D. I do this by lightening the edges of the bluffs, bringing them forward and darkening the mid part of the bluff, making it move backward. With practice the difference to the image is dramatic yet not harsh, the image looks three dimensional and comes alive. Note that this adjustment of brightness had nothing to do with improving the technical aspects of the image and everything do do with the aesthetic qualities.
Sometimes you don't want things to 'stand out'. This is your opportunity to make them recede into the image and become less important, less obvious and specifically less distracting.
You could simply burn them in by whatever method but in doing so the whites remain white, the darks go to black and all you have done is increase the overall contrast and make the feature more obvious. I find that if I drop the white point down so that in the area selected there is no white, this is more effective - while this would result in a very muddy print were it applied to large areas, when selectively applied, it can be very effective. Occasionally I will even move the black point up so there are no dramatic and pure blacks. Since I have done this as a layer and mask, I can use the opacity slider for that layer to 'tone down' the effect I have just created - this is a lot better than 'undo'ing or 'fading' the effect.
On the whole, I prefer the edges of the print to be a little darker than the centre - note the word LITTLE - if you can see it, it's too much, it should only be noticable in comparision with the undarkened edges by clicking the layer on and off. I have a particular aversion to skies so darkened in the corners it looks absolutely fake.
You will note that I have said nothing about colour, saturation, temperature etc. That's a topic for another time.
The only way to learn the technique of tone adjustment is to do it lots, to overdo it so much you have to start over, to make prints and see the effect, to hang a print for some days to see if you can live with it - what works at 1:00 in the morning often looks hidious after a good sleep. Nice bright contrast that gave the image snap at the time looks vastly over cooked afer a week on the wall.
Unfortunately, by and large I simply keep adjusting parts of the print until the image works (whatever 'works' means). Knowing what is right is based on experience, not only experience of working on your own images but looking at that of others. I've said it before but anyone working in black and white should have a subscription to Lenswork Magazine. For colour work consider "Outdoor Photography" from Britain (available at Chapters and Indigo here in Canada), and possibly Focus Magazine which seems to add more colour with each passing issue. "Black and White" magazine shows a lot of good photography, it's printing quality is improving.
Get to every show you can reach. Check out archives of local galleries, museums and universities to see if they have any collections worth looking at - this often requires permission but can be very rewarding. I was at a local group show on the weekend. Workshops are a terrific source of images. Not only do you get to look at the work of the instructor(s) but almost always there is a print critique at which you can see work of the other students. In any mixed group you see images that are techincally excellent and completely boring to images that look like they were taken with something out of a cerial box yet the camera was pointed at something wonderful. In every group though there are some gems which are both technically good and aesthetically rewarding.
To my mind the most interesting photographs are taken by people with an art background who move into photography and immediately start shooting interesting pictures, even if technically it takes them some time to come up to speed (usually a hell of a lot faster than the usual hobbyist who gets side tracked by equipment issues and experimenation with films, developers, papers, printers, computer programmes, and plug-ins.
As I too came through the hobbyist route and am most certainly guilty of experimenting in my youth (before age 50) with all of these time wasting paths, I am certainly raising doubts about my own competency. I can only say that any skill I do have has been acquired the hard way and explains why I'm where I'm at at 57 instead of 25.
There's no time to waste, select some reputable tools, stop worrying about whether they are the ideal ones (they aren't - there are no ideal tools - every tool is a compromise) and really learn to use them.
Well, I did ramble on a bit and got off topic, hope it sparked something for you.