If you could give one piece of advice for roombox/photography...

I'm not much of a photographer but my one piece of advice would be to have good lighting. The lighting can make a real big difference.

 

I’m also not a pro but agree with the person above that lighting makes all the difference. If you have low budget you can start with a very cheap ring light for example.
I also use fabrics for background coz they are big and easy to store. Until not so long ago I was using old bed sheets!

 

I'm by no means a pro, but I think having layers and depth to the shot makes a big difference. I think you can get away with a really small setup (or at least I do) so long as you have fore, mid, and (less necessary) back ground elements. I like to have a very narrow depth of field so I get a lot of bokeh as well, but that's down to personal preference.

My roombox setup is very small, it fits in the space behind a door, and it's not well lit, its far from the window in a north facing room, but I still get some really nice photos out of it, and thinking on it I think it's in part because I usually frame my shots to have objects in the foreground.
Here
And
Here
Are a couple examples of shots taken in my roombox corner with that in mind.

 

I haven't been able to take room-box/diorama type of photos in a while. But when I was still taking them, one thing I've always found useful is to make sure the scale of the props are correct and appropriate. I once had a pie candle that I thought was more 1/3, but was in reality more of a 70+. The resulting photos made the dolls look like they've baked a pie in a giant deep-dish pizza pan. Way too big.

If you can't find proper-sized props, consider playing with foreshortening to make up for that. Sometimes the size discrepancy isn't very visible in real life, but they sure show up on photos.

 

If you've gone through all your set up for the "perfect" shot, save yourself later regrets by taking way more photos than you think you could possibly need and from as many different angles as you can.

 

Taking test shots as you setup the diorama, to check where the edges of the scene cut off, how the furniture is arranged for the angle of the shot, how the proportions & perspective are working, if it's too cluttered or needs more props to soften the flat photo backdrop images... Digital cameras have been a huge help for checking how images are working or what needs corrected in the setup. And I second taking lots of photos. Easier to go through & delete those you don't want than to be disappointed that you didn't quite get a good photo.
Also try lots of different camera angles. Get down on the doll's level. And be in a stable position unless you're using a tripod so your body isn't shaking the camera at a crucial moment.
I love to leave my dioramas/rooms setup for several days so I can take photos with different lighting or change poses & check the photos I've taken to see what has worked or what I want to change or try differently.
And having extra fabric on hand to hang at the outer edge can be handy to soften that last smidge of space or pull up to block the outside world when a shot works better in a direction you hadn't set up the room to include. ;}

 

Hahaha thank you so much! I appreciate that a lot!

 

I don't have a photo roombox for dolls (yet), but I'd say that you can apply a few general principles when designing this space.
Try adding interest with different textures, shapes, and sizes, but keep in mind what style and color palette you're going for so everything goes well together.
Make sure you have some good white light (natural or artificial). It can be more or less intense depending on mood of your photo, and you can also add a cozy/dreamy feeling by adding fairy lights.
You can look up art composition rules and examples, because these also apply to photography.
It's best to avoid making it too cluttered, and cthulhu's hint about taking test shots to see how it looks in the frame is definitely very helpful!

That's more than "one piece of advice" whoops

 

In addition to general good light, thinking about the direction of the light is important if you want something to look like a realistic indoors scene. Typically the main sources of light in an ordinary room is going to be through windows and roof lights.
Making sure that the light is directed somwhat from above or the side and pay attention to where shadows fall under furniture will help alot. Look around in your own home to see what things look like in reality.
Even if you use special photo lights to take the picture, having an idea of what lightsources they are ment to represent in the dolls world is a good idea.

A related tip is to remember the option of using false walls (and roof) to bounce light off. Especcially if you take a series of pictures that are ment to be in the same room, where you move things around to repressent different parts of the room, you'll need to not just move the lightsource to reflect that but you may need to screen things off out of frame for the light to hit right.