How you position your body and all components of it will make a significant difference. This subchapter will focus on the proper hand, elbow, and standing positions.
Note that I will assume from here on that everyone is a right-handed shooter, as that will be the least confusing, as well as the most directly applicable to the right-handed ergonomics of most DSLR's.
With rifles, your hand that is in front of you (i.e. not your "trigger" hand) does most of the weight bearing and pulling. By this I mean that your left arm supports the weight of the weapon system not only by simply keeping it elevated, but you also pull it tight into your shoulder. When you shoot normally (i.e. at 1/50s + shutter speeds and you thus don't need to apply these so stringently) the majority of the weight of a camera is supported by your "trigger" (right) hand. More specifically the "center of mass" or "center of balance" of the camera is at the body end. This very concept is exactly why lenses that truly require tripod collars, such as 400mm+ primes, have their collars further out to the lens objective (a fancy way of saying the glass end of your lens). This is because that even with a heavy camera body mounted on them, the camera+lens system's center of balance is still away from the camera body due to the 1) heavier weight of the lens and 2) the length of the lens itself, which acts as a large lever.
Regarding the lever piece, think of Olympic gymnasts, particularly the ones that do the crazy flips and maneuvers. I can do all of them myself, too...before I wake up. But they tend to be short, right? And then they tend to assume the cannonball position when doing flips, yes? What this does is reduce what's called their "moment of inertia," or their resistance to rotation. If you have ever watched figure skating, it is even more pronounced - pay attention really closely the next time one does a spin and the skater keeps their legs and arms spread out, and then pulls them in really tight. Reducing the skater's moment of inertia causes them to go from a gentle, elegant rotation to a spin that quickly resemble more of a blur. With the lens' center of balance, the longer it is (regardless of weight, although a large front glass element will add significantly to it) the greater the force (i.e. heavier camera body) that needs to be applied to it in order to get it to rotate.
Going back to holding the camera, it is for this reason that with a longer (and usually heavier) lens you tend to hold it further away (you hand closer to the lens objective) than at the lens mount like you would with a pancake lens. In addition, because you are not also pulling it into your shoulder like you would with a rifle, you use your right hand to support the weight of the camera system and your left hand is used to zoom and/or focus, but primarily to aid in stabilization - it does very little true weight bearing.
Well, when you need to apply all of these fundamentals and get that slow shutter speed shot without a mono/tripod, you will switch that. Use your left hand to support the weight of the camera, and if your lens allows (i.e. isn't a short/pancake lens), open your hand so it is palm up and the length of the lens barrel is resting on your open hand. The base of the palm, also known as the "palm heel," of your hand should be just before the point your lens and camera connect, so that your main support point (think of the part of your hand that does most of the weight bearing in a push-up) is under the camera body itself.
With your left hand or your trigger (shutter) hand, pull the camera back so it is firmly planted to your face (of course with your eye at the viewfinder).
Unlike the old John Wayne movies where they have you believe the proper way to shoot is with your elbow completely cocked to the side (and yes, that was old Army doctrine, too), you want both pointed down and in tight to your body. Normal shooting is whatever is comfortable. For me, a shot from below looking up shows how my elbows naturally find themselves:
But for strict shooting where I am trying to completely milk the most light I can via longer exposures, you want them in tight. Point them both down and rest your forearms on your chest:
Here is also a good angle to really see what I was talking about earlier with hand positioning. My hand is open and elongated along the entire length of the lens starting with my palm heel where the body and lens meet. Also, I even lean down a bit with my torso so more of the movement is restricted - if you lean down and try to imagine your elbows pointing into your stomach, then you restrict vertical movement and add further stability.
This only applies when you are free standing because when bracing - which we will cover in the next section of this chapter - your legs aren’t really necessary for stability (unless the type of bracing requires you to do so: situational dependent, and I am confident you will figure out which of these types of situations are which when you encounter them). Normal shooting should look something along the lines of this
When there is nothing to brace and you have to stand, arch your back a little (if you are familiar with weight training, think Olympic lifts), and lean into the camera, just like before with sitting. This is a very stable position. If you notice my feet, they are slightly wider than shoulder width - after much training in boxing and mixed martial arts (more MMA), I have gotten used to getting lower and wider than normal, so what is what I default to. You may find that even wider than shoulder width apart, as I have mine, will prove to be more stable or comfortable (which in turn leads to more stability) for you. Experiment with both.
Another version of the standing self-stabilizer (which I tend to prefer, and not just because it makes my butt look fantastic), was taught to me when I was learning how to shoot long distance (300m and over) standing up with a rifle. This I call the "Torso-Turn-Hip-Point." I don't know what the correct terminology is, but it works for me when thinking of how to explain it. For those of you that are avid rifle shooters, this position should look very familiar to you. There are a lot of steps, but once it all comes together, you will hear those words and the position will instantly come to mind.
Beginning as you would find yourself in a normal standing position, rotate your torso to the left while keeping your feet firmly planted, so that they become perpendicular to the direction you are "aiming." Then take your hips and "point" them toward your "target" (i.e. to the left). You should feel most of your weight on your left foot. Your left hip will get a really deep stretch as well. Then with your left elbow, tuck it in so that it is pointing directly down to your left hip, remembering to keep your arm flush against your body.
You can also try another position that I personally do not like, but someone might. I find I tend to shake quite a bit doing it this way, however you might have more success than me with it. Getting a good base with your feet slightly wider than shoulder width apart, lean back so that your left hand (which is supporting your camera) is resting on your collar bone. You should really feel this in your lower back. Try a 30sec exposure like this :D . Despite not being able to work for many people, I wouldn't recommend attempting this position unless you are quite limber (what are we talking about again?). Seek your yoga instructor for more information.
Not for the faint of heart.