Disclaimer: You don't necessarily have to take these seriously. You can do whatever you want with your art. I'm just sharing stuff that helped me.

1- Shading

To me, shading is really useful when you're trying to make a realistic background cause it really brings it to life and works both digitally and traditionally. You can also use shading to add lights and shadows.

But please make sure to clean up the shading as well. Try not to get it into areas in which you don't want it to be in, it makes your background look cluttured and ugly. Just use your eraser to clean it up. (it works both digitally and traditionally)

Also if your drawing traditionally, I recommend using a blunt pencil for shading. A sharp pencil starts making streaks.

2- lights and shadows

I often use lights and shadows to make my background feel more real (it doesn't necessarily have to be a realistic background, you can use this on cartoony ones as well.)

When I start adding lighting, I try to pick a light source and then add some light to the objects around it to make it look as though the light is falling on the object. But make sure that you add the light in the direction of the light source or else it just starts looking wierd (unless you want it to be that way)

3- Detailing

To me, adding small details like, scratches on glass, wear and tear on an old object, dust dancing in the sunlight, etc make the background look more beautiful  (or hideous if that's what you're going for. It depends on how you use them.)

4- Adding a variety of colours and textures.

This kinda depends on what you're drawing but if you want it to look more interesting, I recommend trying to add more colours/textures. But don't add too much or else it'll become too ov overwhelming.

I hope these were somewhat helpful cause that's all I could think of. I may or may not update this but who knows!

Also if you want to learn more art tips I recommend watching Solarsands's browsing deviant art series on youtube. They helped me a lot!

Bye!