Edit Edit Edit

By "edit" here I mean "throw photographs away" not "photoshop them to within an inch of their life".
The best time to throw an image away is before you take it. This is sort of hard, though, since we tend to fall in love with subjects and ideas, and we try them out. In the age of digital photography, the cost of failure is very low, so we shoot and shoot. At least, I shoot and shoot and shoot.
Your ratios will vary, but if you're not throwing things out pretty aggressively, either:

• You are awesome
• You are not throwing away nearly as much as you ought
• You are not shooting enough

How much to shoot, and how much to discard, depends very much on context. If you're shooting expensive sheet film, and you're really thinking through your ideas and taking your time, maybe you make keepers fully half the time. It's possible!
If you're shooting fast action (e.g. kids) with a digital camera, when your goal is to make a pleasing record of a family event, you might throw away 90% or 95% of what you shoot. On the one hand, your standards are pretty low so you might keep a lot, but on the other hand you're shooting digital so you're blasting away pretty vigorously to try to get at least one good image of each important moment.
If you're shooting something quick, but for art's sake? Let's say you're shooting a portfolio of fine art photographs of hockey. You might shoot a 100s of images, and keep 1, or none. Your standards are high. The action is fast and unpredictable. Perhaps you're shooting digital so each exposure is free.
The point is, you should always be editing. Ruthlessly and thoroughly. Don't accept a bad image, or a dubious one. Shoot enough frames to get what you want. Go back and re-shoot before you try to save a bad image. If the image doesn't look good in a thumbnail or on a contact sheet, it's probably not going to be worth a damn when you're done with whatever your process is. Ruthlessly refuse to press the shutter button if the image is crap, no matter how much you love the subject. Ruthlessly delete the out of focus images, no matter how pretty the out-of-focus girl is. Ruthlessly trash the 10 lousy shots and only even consider the 1 best one of the set of 11 you shot of that thing. Then throw that one out too, when you realize that the light post is sticking out of the model's head.
Don't try to save a bad image, unless there's no other choice. HDR isn't going to make a bad image into a good one. Punching the contrast through the roof won't either. Oversharpening it? Guess... just guess. NO! NO IT WILL NOT! Sometimes we fall in love with these terrible hot messes, and we spend way too much time trying to make something good out of it. Usually there is something good in there that we've fallen in love with, but if the image is fundamentally bad it's because the badness overwhelms the good. You can't parse the badness away, no matter how you try.
If you ever do manage to save a bad image and turn it into a good one, it's likely because you're a better painter than you are a photographer. Perhaps you should consider a career change?

A Photo

This is one of mine.

It's not a technically strong photograph, prints bigger than about 5x7 would look all fuzzy and icky. It was shot with some 8 megapixel point&shoot up in Tuolumne Meadows.
Anyways, it's one of the better photographs I've ever made. It has good balance of forms, some nice echoed shapes and, of course, a good subject rendered according to the visual ideas of Ansel Adams. Not, I hasten to clarify, that I consider this photograph on par with his, merely that my handling of the composition and final rendering are clearly informed by a lot of Adams' photographs. In particular, the relatively high contrast (far outside what was actually present in the scene) and the deep shadows.
The dark shadows, high contrast, and especially the high local contrast in the clouds and the rock, give a sense of drama. The low viewpoint, looking (as one must) up at the great rock formation, enhances this. If you're interested, feel free to save off a copy and see what happens when you reduce the contrast, or do some "perspective correction" to reduce that sense of looking up.

dualities

A feature I tend to notice in photographs is contrasting pairs. I like them "in balance", whatever that means. Perhaps something like "of nearly equal visual interest" except that's not always true. Usually I see one of the pair first, and its presence is merely balanced by the other which I notice later. This is similar to the notion of "negative space" which is in its own way just as important as the subject, the positive space, but is mostly unnoticed.

• Near/Far
• Left/Right
• Light/Dark
• Up/Down
• Background/Foreground
• Texture/Texture
• Shape/Shape

We like to have things to compare. My eye enjoys echoed visual elements and contrasting visual elements, placed against one another for comparison. A brightly lit subject might appeal more placed against a dark background. Placing a small detail in the foreground enhances the sense of scale and distance to a large subject in the distance. A rough and interesting texture is made more prominent and interesting placed against a smooth texture.

12 Great Tips to Punch Up Your Snaps

No.
These sorts of posts are always terrible messes, giving you twelve useless bits of eye candy you can apply. If you have not mastered depth of field, or bokeh, or HDR or whatever technical hoo-hah you want to deploy, go read up, practice, and just do it. None of these things are hard. By all means, go look closely at photographs you enjoy looking at, pick them apart. What did the photographer do?

• Where is the light coming from?
• Is it soft or harsh?
• What is the angle of view?
• What is the point of view?
• What was done to color and contrast with post-processing?

and so on. Then pick through these things for which ones are important to making you enjoy the image. Technique probably plays a role in your enjoyment, it's rare that a subject alone is enough, so figure out what you like.
Then go practice those techniques a little. Really, it's not that hard. If you really want a tutorial on bokeh, google "bokeh tutorial" and you'll probably find a dozen. They won't tell you anything you don't know, or could not have figured out in 30 seconds of experimentation.
Similarly lighting, photographs posted on flickr or wherever with "strobist info" drive me wild. If you need a little diagram of the lighting setup to see what's going on, you're simply not looking at the photograph. Look at the result, it's all in there. By definition. If the result of a light isn't visible in the photograph, then that light isn't necessary anyway.
Here's some general guidelines and ideas for making a photograph that connects with the viewer:

• How does the scene make you feel? What about it makes you feel that way? Shoot that.
• Is there a story in your image? Tell it in one frame. Well, shoot many frames, but pick the one that tells the story.
• When in doubt, put people in it. People are interesting.
• Be enigmatic, if nothing else. Make the viewer wonder, but try not to let them down. See also putting people in.

The Online Photographer

Mike at ToP rules from orbit, but sometimes he or his guest writers wander off into technical mucking about with resolution and sharpness and gear and so on. So, it's always a joy to see essays like this one.
Read it. Live it. It's the truest thing I've read about photographs on this whole ugly internet thing.

An OWI Photo

Here's a photograph from the Office of War Information:

Nice, huh?
Two human figures, one on each side. Two balls, one on top of the other, in some sort of column. Some interesting stuff in the background, that's not too distracting. I think it's printed a little too high contrast, there's a lack of middle tones and an overall harshness to it. Still, the textures on the ball-things that the men are leaning on/climbing are striking and awesome.
This is a great example of balancing forms and areas. Left/right we have the two soldiers, who are in the bottom half of the frame to contrast with the sky above, and we have the two ball forms up and down as well. There's a natural focal point, which the two men are more or less facing, and which isn't quite centered. There's the end of a third ball at the top of the frame, to close things up visually there. There's some things wrong with it, but it's a very strong image. As for engaging the mind, well, there's a whole lot to wonder about, isn't there? More or less, who the hell are these guys, where the hell are they, and what the hell are they doing there?
Evidently they have scaled the scaffolding (see those sticks in the background?) to the top of the Taj Mahal. They appear to be sitting on the base of the finial.
Where's the photographer?

Shoot what you feel

Look at other people's photographs. Famous photographs, things your friends have shot, anything. How does a photograph make you feel? How do you react?

If it makes you think a little, or feel a little, beyond the usual "what a pretty flower" or "what an awesome HDR", try to figure out why. What is it in the image that makes you feel that way?

Some elements of the visual vocabulary:

• Darker vs. Lighter
• High contrast vs. Low contrast
• Color temperature (this applies to B&W too, as tonining)
• Where is the subject in the frame?
• Point of view (low, high, left, right)
• Angle of view (wide, narrow)
• What is emphasized, and how?

This might seem like art nerd wankery, and it is, but if you can learn to read the language a little, you've got a better chance at speaking it.