For house interiors, the biggest limitation in your kit is the lens: 28mm on a Canon 20D crop body is usually too narrow for small rooms. A wide or ultra-wide lens is the most helpful upgrade, since it lets you show more of the room without backing into a wall.

Use a tripod and stop down for good sharpness and depth of field. Interiors often need blending window light and room light to keep the image bright and natural; subtle HDR or exposure blending can work well if done carefully.

Try to keep the camera level. Tilting up or down causes converging vertical lines, which makes walls look like they’re falling over. A tilt-shift lens is the ideal solution, but it’s expensive. Practical alternatives are shooting from a higher position while keeping the camera level, or correcting perspective later.

If you can’t get a wider lens, stitched panoramas are a useful workaround. They can create a much wider field of view, help with perspective correction, and produce very detailed files. A tripod helps, and a pano head/software can improve results.

In short: prioritize a wider lens, use a tripod, keep the camera level, and consider exposure blending or stitched panoramas for the best interior results.