Here are some random yet useful tips:
Take a large trash bag and go around the house/apartment and dump the trash in it from the smaller trashcans.
Flowers do wonders for adding beauty to any room!
Vacuuming can refresh a room.
Dusting can refresh a room.
Painting one wall a different color can add to the room. (Accent walls)
Most places that sell plants have signs telling you which plants grow best in your home or outside in the yard. And how much sunlight they need.
Sometimes a love seat that seats two can be better than having a couch. If you have limitedspace.