There are many things that you should carefully take note of; here is an example of what to look at in every room.
Furniture placement is carefully done by a stylist to maximise the appearance of the room size. Is there enough room for your furniture?
Rugs are often placed over timber floor areas. Rugs can help with suppressing flooring noises and assist in creating visual warmth in a room. Rugs can also be used to hide floor damage; I suggest you always take a peek under them.
Doors held open by magnetic door catches should be closed to check that the door actually shuts and is not binding on the floor or door frame. I often find that many doors do not shut when tested.
Windows are often shut, as refrigerated air conditioning units do not require them to be open. This often results in awning or sash timber windows being painted in the closed position prior to the property being listed for sale and making them unable to be opened. Most people like fresh air at night when the temperature is nice, so this should be an option. Having to have the windows forced open, can damage the timber frames, resulting in the new owner having to remove the opening sash or awning windows to resize them to be able to be closed and to paint the frames. In an older house, this may be quite time-consuming and expensive. I find this to be very common to most older homes.
Aluminium windows and doors also commonly have issues with the sliding roller mechanisms or the solid slider blocks that may require maintenance or replacement.
Modern (timber look) uPVC tilt and turn window frames can be damaged on the outside of the window by small stones thrown during lawn mowing. If the house has any lower window sections, it is best to check for damage.
Ceilings are commonly painted in a matte white paint to achieve the best appearance; it can also assist in hiding deformed ceiling issues such as sagging or popping of the nail heads.
You should also check inside built-in robe areas, as often the rear wall areas may back onto an exterior wall or bathroom. When renovating for a sale, the vendor frequently doesn't paint the areas that aren't visible. These areas may also develop mold and other types of wall damage, such as rising damp, due to leaking bathroom plumbing or drainage issues.
You should check electrical switches and power points to ensure they are serviceable and adequately fastened to the walls.
Termite damage to wall framing, window frames, architraves, skirting and flooring areas is also an area of concern that requires a thorough inspection. Tapping can show hollow areas; looking for filled-in areas is another sign. Ideally an inspector will have a moisture meter, thermal camera, and a termite radar unit to find wall moisture locations and if termites are inside the wall framing.
It takes time to look everywhere in every room, this simply cannot be done when you look for 15 minutes at an open house inspection.
This list is just an example of what is commonly investigated during an inspection in each room of the house you are looking at. Then the ceiling space is investigated, and the on-roof inspection is done looking for flashing issues, cracked tiles, guttering areas etc. The external walls, eaves, fencing, garage area, timber external structures... It takes around 90 minutes to investigate a moderate sized house, longer for multi storey or large houses.
This list should help you in what to look for, but as always, I would suggest you have the house inspected by a qualified, insured building and pest inspector.