Choosing the angles
Even though you are photographing everything you can see from one point,
there are benefits to be had from carefully choosing where you point your
camera for each shot. For example, lens flare can be a big problem and there
are generally two approaches to this.
Shoot one image with the sun in the middle of one frame. If you're using
a circular fisheye and shooting 3 images then you will only have the sun in
one image, the lens flare will be directly above and below the sun and not
at some strange angle, and you will also have a seam that runs through the
shadow of the tripod making it easier to remove your own shadow.
Another approach, most often seen in IPIX panoramas, is to place the sun
at the edge of an image so that the two adjacent images get a similar dose
of lens flare. Having the sun in the picture will invariably create an
image with different contrast to the rest of the panorama. I prefer the
first approach, giving me a broad area across which to blend the contrast to
match the adjacent images.
Reducing parallax errors
OK, in theory if everything is set up perfectly you don't have parallax
errors... but one way to minimise them is to shoot directly at the
things that are closest to you. Placing them in the middle of the
frame and away from seams reduces the possibility of parallax errors.
Footprints and trampled grass
Many people set up their tripod, shoot the panorama and then shoot the
nadir patch to remove the tripod. By this time there are footprints
all over the place, or a circle of squashed grass from where you've walked
around the tripod. Figure out where you're going to put your tripod
and then shoot your nadir patch before setting the tripod up and making a
Stand at 90° to the main light source (usually the sun) when shooting the
nadir patch image to remove your shadow.
Edge to edge sharpness (or lack of it) can be as much of a problem as
light fall off. For this reason it is important to shoot at an appropriate
aperture to maximise sharpness. Circular fisheye lenses are generally quite
soft around the edges at apertures wider than f8. I could supply sample
images but I won't. Test your own lenses to see what YOUR optimum apertures