What I find interesting is to pick an object - it could be something rather ordinary. The challenge is often not in building the model(s) - although this certainly can be - , but in making them look good. Strive for being able to identify and incorporate subtle details. Then, build a scene around it. I started out with a spoon once, and ended up with an entire scene that looked like the inside of a small (older) apartment. I have a another scene where I started out modeling a student’s desk (like you might find in an elementary or middle school), and ended up with a classroom scene- complete with two students.