Tip 1: You need a good digital camera with a tripod. When photographing an interior, you want to make sure that everything is clear and sharp. I use F11 (aperture) and 1/2 second (ISO 200) in most cases. Sometimes if you want to get a blurred background on a close-up shot, then you will want to shoot with a wider aperture, or the smallest f-stop your camera will allow (e.g. F1.8).
Tip 2: Use a wide angle lens. Shooting wide can make the room look great, especially when in Hong Kong, the size of the property is most likely less than 100 sq. meters. In a confined space, sitting tight into one corner while you try to get the other three corners in just looks wrong. You shouldn't shoot all three walls into one picture. Showing the highlights of the interior design features is important. About the lens, anything in the 16-24mm range on full frame (or the APS-C equivalent which equates to 10-16mm approx. on some less expensive camera) is great. I often use 17mm full frame for my wide interior work.
Tip 3: Sufficient indoor and natural lighting are both important. Light up the room. If there is good natural light coming through the windows, use that as well. Adjust the overall feeling of the lighting to a balanced and optimized level.
Tip 4: Find the best angle. Take time to explore different angles to shoot from. Decorate the room with small artistic items, plants or anything you like to add a bit of creativity. We can't all afford a tilt-shift lens to keep perspective in check, so it's a really good idea to shoot with the camera at or slightly above mid-room height. This means you can keep the camera aimed out straight to keep the walls vertical. While the perspective distortion you get can be corrected in post-production, it's much easier to get it right in camera. This is another reason to use a tripod as well.
Tip 5: Use post-processing software, e.g. Photoshop or Lightroom. You should bring the Highlights down and open up the Shadows. Next bring the Blacks down to ensure that the contrast lost from opening up the Shadows doesn't impact the image too much.
Tip 6: Go vertical for staircases and other special feature. This is also important if you want to share the pictures on the web, as most images are horizontal in the interior photography world. Some vertical images could light up your portfolio. Verticals usually mean letting the eye fill in gaps, so make use of the composition to show hints of the room.