Bad Advice for Photographers
Not all the advice available for photographers is good advice. You may not want to do the exact opposite, but you should understand the full story so you can make up your own mind.
Buy the Best Camera You Can
A camera is obviously important, but it's the lens that makes the biggest impact on image quality. You are much better off buying a mid-range camera and saving your money for better lenses. A camera is just a fancy light-tight box. It's the lens that focuses the image. Think of it this way: would you rather you rather have eyeglasses with really nice frames but cheap lenses, or the other way around?
f/8 and Be There
The old mantra for getting good images of "f/8 and be there" may work well enough for news photographers, but it's horrible advice for outdoor photographers. Your choice of aperture should be determined by how much depth of field you need to cover your subject. There are no right answers. You have to evaluate the situation and think about it.
Stop All the Way Down for Maximum Sharpness
Sufficient depth of field is hard to come by when shooting macro subjects. Things beyond the useful depth of field will appear progressively blurry, so many macro photographers tend to stop their lenses down as far as they can go and shoot at f/22 or even f/32 to maximize sharpness. Landscape photographers sometimes do this as well for that "Ansel Adams grand vista" look. But if your aperture is too small, you can actually make things worse. The term "diffraction" describes the bending of light rays through a small hole (or close to an edge in general), and it can start to affect sharpness beyond about f/16 on a DX sized sensor. As with "f/8 and be there," your best bet is to choose an aperture based on the depth of field you need. Don't just ratchet it all the way down without considering the consequences. If you want good depth of field for landscapes, learn how to use hyperfocal focusing.
Fill the Frame with Your Subject
While this may indeed be good advice sometimes, it often isn't. Many subjects look much better if you give them a bit of room in the frame, both to provide some context and to avoid that "crowded" feeling from having them bunched up too closely against the edges of the frame. There's no surer way to make wildlife look like zoo images than to crowd them in the frame.
Center Your Subject
My old Kodak pocket guide on how to take vacation photos advised trying to center the subject to minimize the chances of accidentally cutting off anyone's head or arms (figuratively, of course). Somehow, this became the prevailing advice in some circles for all types of photography. I suppose if you were a careless photographer who tends to hand-hold, you might be able to justify the bulls-eye strategy, but for most of us, this is horrible advice. If every photo you take looks this way, they will tend to look somewhat boring and lifeless. Placing your subject partially off center will lead to much more dynamic and pleasing compositions.
Always Follow the Rule of Thirds
Having learned the lesson of not always shooting every image with the subject dead center, most photographers next tend to adopt the "rule of thirds" strategy which dictates dividing the frame up into thirds both horizontally and vertically, and then placing the subject at one of the intersection points, or at least along one of the thirds lines. While this may be better than the bulls-eye approach, it can still lead to results that seem repetitive and unoriginal. Your best bet is to start with the rule of thirds, but then recompose from there if the situation warrants. You're the photographer. Look at the scene, and go with what seems right to you. If you like it, the chances are that other people will as well.
Shoot with the Sun Over Your Shoulder
That same beginning Kodak pocket handbook advised to always shoot with the sun over your shoulder so that your subject was front lit. If you needed full, direct light to achieve an adequate exposure, this may be warranted, but frankly, that is seldom the case these days, even if it ever was. Flat, direct lighting hides a great deal of the surface texture of a subject that would be otherwise visible when the light source came from more of an angle. And if your subject includes people, they really won't look at their best when squinting into direct sunlight. Trust me.
Shoot from Two Hours After Sunrise Until Two Hours Before Sunset
This one, too, is more "helpful" advice from the early days of Kodak that has somehow persisted over the years. Presumably, the idea here is two-fold. First, this would help ensure you had adequate light, but it would also minimize color temperature shift from the low angle of the sun within two hours of sunrise or sunset. But at least when I'm shooting near dawn or dusk, I want that "golden hour" glow. Indeed, such times tend to be the best for nature photography, not the worst. And if adequate light is your concern, get a good tripod, and use it.
Make Sure Everything is Well Lit
For some reason, many instructional guides for aspiring photographers seem to think that shadows are a bad thing. If you judge exposure based on the histogram, you may believe you should aim for a "bell curve," without the graph bunching up on either end of the scale, pure black or pure white. But while burned out white highlights are clearly best avoided, I disagree about the shadow end of the histogram. The real world has shadows in it. Shadows provide drama, emphasis, and even mystery in a composition. They are something to be embraced, not shied away from.
When in Doubt, Overexpose
If you go back far enough in my involvement with photography, way back when I shot snapshots on print film, the advice was that, when in doubt, overexposing an image was better than underexposing. This related to the fact that print film was reversal film, creating a negative image that was then inverted, light for dark, when printing. But even slide film didn't work that way, and certainly digital imaging doesn't. Both create a direct, positive image, and overexposing either is much harder to correct from that is underexposure. Overexposure with digital photography can be especially problematic. Once you burn out an area (red, green or blue channels, or particularly all three) to the highest value possible, all detail will be lost. Nothing can recover it since it would have never been recorded in the first place. While digital cameras do suffer somewhat from noise at low exposures, newer sensors can tolerate underexposure much better than early sensors did. In today's world, there is little reason to worry about a slight underexposure, and every reason to stay well clear of excessive overexposure.
You Can Always Fix It Later
One last bit of bad advice that we need to set the record straight on. Far too often, photographers fall victim to feeling that they can always "fix it later" in Photoshop. While many types of image optimization are not only possible but desirable in the digital darkroom, not everything can be fixed. And you are almost always better off getting it right in-camera to begin with. Even just on the simple basis of time spent slaving over your computer versus being out shooting, the less you have to do to an image in Photoshop (or Lightroom) the better. Hopefully, you're reading this because, first and foremost, you want to be a photographer, not a Photoshop guru.