Once the new shots have been downloaded to my computer, my first task is to weed out any junk, garbage, and crapola. If a shot is too far gone in one of these four areas, I almost always delete it. Even if I don't delete it, it's probably never going to be seen by anyone else. So here they are...
This is the one factor that never changes order. I always consider the focus first. Every time. If the focus is off, nine times out of ten I delete it unless I have a specific reason for saving it. I don't care how good the other aspects of the photo are, I won't be happy if the focus is bad. I don't know how many times I've come home excited about my outing only to discover several shots that were blurry or had soft focus. And the LCD screen on the back of your camera will lie right to your face! Out of focus shots will often look okay on the LCD screen, but you see their true nature when you open them on a computer. The best way to check focus on your camera is to enlarge the photo so you can see detail on the LCD screen.
When I talk about focus, that doesn't necessarily mean everything throughout the entire photo has to be in focus. You as the photographer determine what it is you're focusing on. But if the subject of my photo, no matter how large or small, isn't focused properly, then I don't use the shot. In the past, I have shown photos here and there that I knew weren't in perfect focus, but I've become much stricter on myself. If the focus is sharp, I can sometimes let some of the other three factors slide, but even if the other three criteria are perfect, they won't make up for a blurry shot.
I'm tough on myself about composition. I could even be borderline OCD about it. When I'm critiquing my photos, composition ranks above exposure. After focus, composition can make or break a shot. I love the rule of thirds! This is probably the "rule" I follow most strictly. Not that it can't or shouldn't be broken. I've done that, too. Photography rules can be broken with great results when done properly. For the most part, though, the rule of thirds will give you a nice composition. Our eyes naturally look for smooth, flowing, pleasing compositions. Have you ever seen a photo that just looked awkward or "off"? Did you think to yourself, if the photo had just been framed this way or the subject was over here a bit more it would look better? I see photos all the time when I'm browsing 500px or Flickr that are outstanding in every way, but the composition is wrong for me. That doesn't mean it's wrong for everyone, but I'll look at a photo like that and it's just not pleasing to my eyes.
If I didn't frame a shot the way I intended or I missed part of my subject because it was moving (birds, animals), I generally won't keep the photo. If the subject is leaving the frame rather than entering the frame, I usually won't keep the shot. If a photo just doesn't look balanced to me, I am probably not going to use it. It's difficult to describe what I'm looking for because each of us may see things a bit differently. You know what looks pleasing to you and what doesn't. Composition can either draw us in to a photo or make us want to move on to the next one.
There was a time when exposure would have been my number two criteria, but the digital age has changed that. For me to delete a photo due to exposure, it has to be really off. If it's that bad, it means I really screwed up when taking the shot. My photos aren't always perfectly exposed, but they're usually close enough that I can make the necessary corrections during processing. Since I shoot in RAW, I have to process my photos in order to get a final product so adjusting the exposure isn't a big deal. If I do get a photo that has been exposed incorrectly, it's usually too far underexposed. When you have a badly underexposed photo and you attempt to correct it in processing, it will add digital noise to the shot. Depending on the ISO setting, the additional noise can be very noticeable. Proper exposure is hardest when you have a scene with both really light and really dark areas. If my main subject is just too improperly exposed either way, I'm not going to use the shot.
When I consider the background, I don't mean just the area behind the subject. It could be anywhere in the scene. Part of this goes back to composition, but if I find something in the shot that is distracting, there's a good chance I won't use the photo unless I can crop it out. I've downloaded photos and found litter in a shot that I didn't notice at the time I took it. Sometimes the subject blends in too much with the background or the background is very busy and distracts from the subject. I always try to take these things into account when I'm framing the shot, but sometimes I miss something or it's physically impossible to leave something out. Power lines, light poles, buildings, signs, vehicles, roads, trash, and people are all things that can be annoyances in a scene. If I can't frame something out of the photo, sometimes I'll take the shot, anyway, and then make a determination later whether or not to keep it.
Below is an example of some of the things I'm talking about. There's almost nothing right with this photo. The focus is off. The feet are in focus, but not the head. Exposure on the heron is a bit dark, but I could correct that. The heron is flying out of the frame rather than into it which drives me crazy. And who could miss the tree in the foreground? I was panning along taking several shots as the heron flew by so this wasn't the only photo, but it's a good, albeit obvious, example of what I look for. For me to like this photo, the whole heron would have to be in focus, I should be leading it enough so it's entering the frame, and there would be nothing else in the shot.
So those are the four criteria I use when deciding which photos I keep and which ones get sent to the digital graveyard. Focus is always number one and if that's acceptable, I then look at the others. If you've managed to read this far, keep in mind I'm rather tough on myself. This is how I judge my own photos. Ideally, I try to get photos that have good focus, nice composition, correct exposure, and no distracting background elements. Unfortunately, it doesn't always come together that way. But that's what's nice about the digital format - hit delete and try again. Mistakes are free and when I make them, I delete them and move on.
Since I mentioned 500px and Flickr, I would urge you to take a look at the photos posted on both sites. 500px is my favorite. Check the Animals, Nature, and Landscape categories. Some of the photos are just incredible! Browsing these sites makes me realize just how inadequate my skills are, but they also give me motivation to keep trying.