For example problem 1, if you photograph a room with a super-wide lens (like the Canon 11-24mm f4L USM) items and furniture like sofas and televisions warp and stretch horribly in the corners – (don’t even try this lens on people!) So, you often have to rearrange a room through the lens, moving furniture more centrally, whilst trying to keep lines perpendicular. Whilst a room layout may be perfect for a guest, it may look messy and chaotic through a lens – especially one as unforgiving as the 11-24mm.
As a result, I usually arrange a room within the central 80% of the image, and then crop out the sides. This lens is also so wide that it can almost see round corners (really!) and actually chopping parts of an image out, and not showing the entire room actually gives the impression the room is larger than using the whole of the 11mm wide angle view.
I always shoot interiors a f14/f16, and will use a fast prime like a 35mm f1.4 for little details, blurring out the background. Shooting at f14 and a low ISO means shutter speeds of around 1/2 second. Obviously a tripod becomes essential for such long shutter speeds, but it also helps eliminate issue no.2:
Photographing straight on: Don’t use a tripod to get your horizontal line correct, just to then photograph slightly up/down into the image. What looks normal to your eyes, looks very unappealing and weird on a screen. Shoot straight in all directions! This often means changing the height of your tripod for each shot, to keep all lines straight whilst being able to look over tables, beds and countertops.