If it is an option, always enlarge your windows and openings; when possible try to add your balcony, small terrace, even side garden into your interiors by using folding glass and designing the indoor and the outdoor together (same ceiling, etc).
Always use a lot of very light colours
In key areas place a large decorative mirror
Do not clutter the space and keep a lot of the items in hidden storage when possible.
What type of furniture is suitable for smaller spaces? What type of furniture to avoid?
Look for light pieces; a light couch and two wooden chairs (Danish in design for example); try not to put 2-3 couches around your main seating area this will just close up your space.
Avoid large bulky couches, they tend to clutter the space, look for couches 70cm in depth or less; often when sofas have back cushions (not throw cushions) they tend to be deeper and bulkier
Does one have to minimize the use of home accessories in smaller spaces?
I would use home accessories but not in excess 1-2 decorative items per table maximum, try to make them large enough to have impact but not large enough that they dominate the piece they are sitting on.
Artwork should also not be excessive as it is the light walls that will make you feel the space and give you a grander feeling.
What colours make a room seem bigger?
Light coloured walls (white or off white, or a very very light warm taupe) on the walls and ceilings and often try to keep the ceiling and the walls the same colour
Avoid colder colours; cold greys, cold blues; no matter how light.
How should one arrange lighting in smaller spaces?
When lighting small spaces, always try to light the walls and the ceiling in an indirect way that makes them look brighter
If you have an any bit of outdoor, try to light it with you as well, so that at night it looks like a natural extension of the space.
What mistakes do people fall into when designing small spaces?
Often the idea of how to make the space feel bigger does not enter peoples mind when they are furnishing, they make sure that what they have fits in the space and don’t realize that small spaces call for a bit of a change in lifestyle. Minimalists will always be able to make the best use of small spaces.
Also often there are small construction tricks that people can do to increase the size a little bit that make a big difference that people do not think about, for example:
Re-arrange the actual layout, making it more open, lessening the number of doors
Removing all false ceilings
Including balconies into the plan or at least integrating the outdoor into the day to day living
Tightening the plans, removing any excess space from extra closets, and unnecessarily large bathrooms