Lens flare is visible in a couple of ways. The type most digicammers are talking about are obvious internal reflections of strong light sources within or just outside the image. That's hard to fix with a lens shade, but multicoating helps (and the problem is more pronounced with some lens designs versus others). Given that it may be unavoidable, many just make it part of the composition.
Then, there's veiling flare, where light inside the camera bounces around and causes an overall fogging of the film in addition to the image-forming light. The light inside the camera either shines directly on something other than film and reflects, or it reflects off the surfaces of the film itself and then bounces around.
Two strategies for minimizing veiling flare are: prevent it, or absorb it. Absorbing it is why the inside of the camera is as non-reflective as possible. That's why the backside of quality lens boards are flocked or painted ultra-flat black, and why the inside surface of bellows is fuzzy rather than smooth and shiny like the outside.
Prevention is where shading comes in. The most efficient possible shading strategy prevents light that won't fall on the film from entering the camera in the first place. The shade, which will be out of focus if the edge is in the picture, casts a fuzzy shadow inside the camera, so it's impossible to trim off all extra-image light. But a good shade allows the photographer to minimize it as much as possible. The best strategy is to use a shade that is adjustible on all sides to just avoid being visible through the lens aperture (that's one things those clipped corners on the ground glass are useful for). Sinar makes an adjustable mask that mounts on an accessory standard in front of the front standard, with a bellows between it and a rod/clip holder (as Frank described) on the front of the front standard. Using the accessory standard makes it possible for the shade to follow the movements of the camera precisely.
Next best (and about as good as anybody else produces) is what Frank described, which is mounting a spare bellows on a hex rod using two clips. The front edge of the bellows can be extended or retracted to accommodate different focal lengths. Sinar even makes a jointed rod to allow the front of the bellows to be aimed to follow the movements of the camera, though without the same precision as using an accessory standard.
(By the way, the front standard used on the F and F1 is intended to serve as the accessory standard on P cameras. I have an old Norma-era accessory standard which is lighter and more compact for this duty, though I've never gone that far with shading.)
A bellows-type shade that can be expanded or contracted is called a compendium shade. They are extremely effective.
But it is ironic that the cameras provided with the most effective shading strategy usually have the best control of in-camera reflections. Thus, I suspect the effects of that level of shading in practice will be pretty subtle.
At the other end of the effectiveness scale, the one essential element of shading is to prevent strong light from shining directly on the front surface of the lens. (Strong means in relation to the scene and exposure.) For most outdoor photographers, that means keeping the Sun from shining on the front of the glass. If it does, it will illuminate every spec of dust, haze, and microscopic imperfection brightly, which will create the most severe sort of veiling flare. That's the kind of flare that is easy to prevent with a hat or a dark slide.
For most black and white photographers, the subtle veiling flare that remains after eliminating the flare from the Sun shining on the lens lowers contrast slightly. That's easy to correct in one's contrast control workflow, so it isn't really that important in practice. Super-effective shading strategies were developed for commercial work using color transparencies intended to be used for advertising process color, and in the days before Photoshop the slide had to be just right straight out of the camera.
So, all that long-winded context comes down to this: The best shading is the most that you will do every time without resenting it. Sinar's bellows clips and rods make it easy enough to use a compendium shade in routine practice, and easier than most any other accessory shade. It's not easier than a hat, though. A hat is much better than nothing, especially if the Sun is on the front side of the camera.
Rick "who usually uses the rod and clips, but sometimes just uses the hat" Denney
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Originally Posted by Bill, 70's military B&W
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