Carefully choose what you put in it. Measure when buying furniture. Try to have items do multiple duties, as in having storage inside an ottoman. Limit what you have to the essentials.

Use built ins, lighting and wise placement of mirrors opposite windows to add more space to the rooms. All the same rules apply as decorating any other kind of place...scale and proportion is key.

https://www.thespruce.com/make-a-small-room-look-bigger-1976069

thank you everyone for the suggestions. I will keep all of them in mind.