Books, and art on the walls that has been chosen because the occupants like it and not just because they go with the decor. Secondary lighting, nice textiles, - rugs, throws, a plant or two. Flowers are always lovely but only a treat for for me.
I can respond really positively to a huge range of periods and aesthetics but I don’t like look where it’s like someone has just bought the full range from a shop and plonked it in their house. My particular dislike is those vaguely abstract impasto paintings in the same colour scheme as the upholstery or cushions, only chosen because they match.