I try to think AV before pressing the shutter release. In other words I aim to take images which will produce the best possible dissolves and third images. Therefore, the light and dark areas of the images are important. Light areas are the first to appear and the last to disappear in any dissolve. My preference is to avoid large light areas wherever possible. Dark areas are bonuses in that they provide opportunities for good third images. I try to achieve good composition in the images by using the rule of thirds. However, one particular area where the rule of thirds can be detrimental to the dissolve aspect is in the case of horizons where large light areas fill the top third of the image. Better dissolves can be achieved by placing the horizon closer to the top edge of the frame or losing it altogether.
Strong shapes can pose dissolve problems. These may be solved by placing the strong shape off-centre and bringing in a subsequent strong shape through the opposite third.
Similarly shaped objects, which will dissolve, can be placed centrally and deliberately superimposed but this implies an eye for registration either in the mind or the viewfinder.
I usually take about three times as many images as I need to allow choices in order to get the best dissolve. I include close-ups, mid-shots and distant shots. I also take a variety of link shots on location. Link shots are sometimes necessary to effect a suitable transition from one section of the sequence to another, or from one image to another which poses dissolve problems. Link shots can be abstracts or, more usually, close-ups of fairly featureless objects, e.g. doors, walls, water, clouds, etc. through which you can bring almost any image.
Sorting the image order
Before sorting the image order, I view every image separately and reject any that are not up to standard in terms of exposure and quality. I do not subscribe to the view that any old image will do for AV just because it happens to provide a good dissolve.
For any sequence the images from which the final selection will be made are set out in the computer 'light box'. The images will have been shot with a development of an idea in mind, therefore they are grouped accordingly in the 'light box'. When sorting the images, I keep in mind the "aim at the top of the light box", and do not include anything that does not contribute directly to the aim. This helps me to develop the idea without going off at a tangent. It is sometimes tempting to include your favourite image even when it does not contribute to the overall idea or story.
There are usually a number of images which will form the start of the sequence. That first image is important, the opening of any sequence is a statement of quality and intent. Having selected the first image then all the suitable candidates for the second image are then compared for suitability and dissolve potential. When selecting these suitable candidates, due consideration is given to light and dark areas, shapes and colour balance.
The process is repeated for each subsequent image selection. Be prepared to alter the order of the images if you discover better dissolves between non-adjacent images.