-Choose a theme for each room, and stick with it (my GH has a library and an indoor garden maze). Build on those themes when you are able to. It's real easy to go broke buying a lot of furniture, so ditch a theme because you are low on gralats; save up awhile so you can go on another shopping spree.
-Sometimes, new furniture releases can be worked into the theme.
-Basic furniture like boxes and chairs can be used as building blocks for creative structures (like boats as mentioned).
-Sometimes, basic furniture is just fine to provide a simple "Graal" look.
-Flower pots, plush toys, and other small things provide for good accent pieces.
-A few well-placed rugs look good. Rugs can also be used to hide railroad track.
-I like putting things such as statues, torches, or flower pots on either side of a door way.
-You dont have to put all the furniture on the floor. Its okay to put cosmetic furniture in the walls so there is more walking space.
-I personally dont use weather crystals because they are distracting.