The two biggest challenges when shooting indoors are
- Content (especially for real estate)
And these are the two areas that, I believe, have the strongest impact on the final result
Let me explain.
Contrast: When you are indoors, if there are ANY windows in or near the scene (always the case with real estate) a sunny day can be your biggest enemy. The huge difference between the daylight coming in the window and the actual interior lighting is a killer. Also, the difference in color temperature makes it very difficult to determine (manually or in the camera) the proper White Balance.
For this reason a dreary, rainy day is really your best choice to take photos indoors.
Content: It is critical to "stage" the scene before taking the photographs. If there is clutter on surfaces, move it out of the frame. Be sure all the furnishings are square and neat (chairs pushed under the table, for example). Reposition or remove anything that adds clutter or distraction to the scene. Never forget ALL THAT MATTERS IS WHAT APPEARS IN THE FRAME OF THE SHOT.
I cringe when I see a set of Real Estate (particularly residential) photos where all they did was run in the door, go snap, snap, snap with a camera set on auto-flash and run out. The "Presentation" is awful and I am certain the potential sale of the property is affected by that. Just marvel at the care and patience applied to the photos of food for a menu board at McDonald's!
Best of luck.