Guys I think there is some confusion here which I started..:+]
My first post was about stacking and I accidentally asked another question which is about stitching in order not to start another thread.
It is not clear to me if you want to stitch to get greater coverage, or if you want the same coverage at higher resolution. If you want greater coverage, the same focal length will work. If you want the same coverage with greater resolution, choose a narrower lens, like perhaps a 35mm or a 50mm. In either case, choose a lens with the lowest possible distortion, since otherwise you lose resolution when the software corrects the distortion before stitching.
Either way, the best way is with a pano head. Some pano heads have balls in the pivots which "click" at specific angles (12 degrees, 15 degrees, ...). You must learn how many clicks to turn between pictures, for the lens that you are using, so that you get about 30% overlap (horizontally and vertically!) between frames, as Jack said. If there are no clicks (detents), then you probably have a scale for the angle. Same principle.
If you don't have a pano head, and want to try by hand, then imagine that a point about halfway along the length of the lens, but *on* the central optical axis, is the pivot point, and try to rotate yourself and the camera around that point. This is *really* hard! You could practice in the studio with a couple of objects behind each other, and just look through the viewfinder while pivoting, making sure that the objects always stay behind each other. Try 2x1 (row x column) horizontal, 3x1 with portrait orientation, and stitch with your chosen software. Then try 2x2 horiz., 3x2 vert. and so on. I would not do larger than that by hand. It gets unmanageable pretty fast. However, with the 24mm and 3x2 portrait mode, you should have a very wide coverage, so maybe you don't ever need more. You should get the hang of it pretty quickly. Just make sure to position the images in PS or Autopano Pro and check how much they overlap.
I think only practice will make it easy to do. I have done some experimental 100-shot panoramas (on a tripod but with a normal ballhead), and still managed to miss parts of the scene. Swinging over the scene several times while looking through the finder might help to visualize the passes. Start with a spot in the middle that you can always find again, and use that to choose your rows and columns. In each frame, before you move on, check where you are, and then choose where you want your next edge-of-frame to be, then move. If you lose track of where you were, you can always return to the start position and work it out again.
Two things to be careful of: if you are going for very wide coverage, your rows will most likely converge at the ends, since you are essentially covering a part of a circle. If you don't take care to cover the corners, you might have to crop a lot off the vertical and horizontal edges, towards the center of the edges. So shoot extra to cover the corners. The second thing is to always watch your horizon. It is too easy to start slanting.
The last thing is that the software requires some practice too, so make you sure push some tricky panoramas through on your own time before moving on to selling them Correcting verticals, matching difficult areas with little detail, and other problems will arise.
I hope that helps. This is what I have done, but I am no pro. I have just fooled around with it privately. If everything doesn't make sense the first time, then just work through a few panoramas and things should fall into place.
Here is an example I did hand-held, with an M8 and 50 Lux ASPH, by shooting wildly 36 shots, and I had some problems with coverage towards the edges due to poor planning, so I had to crop. I ignored correcting verticals for this shot. The lens was wide open, so the image has an unusally shallow depth of field for that wide coverage. Two quick shots covered the girl, and then I shot around to get the rest.