/3/ - 3DCG

Trying to take on an animation for a friend. I've got so much to do and so many scenes to get through. It's my first project that isn't from a tutorial.
Pic related is all I've got going so far, I feel too overwhelmed already and have no clue where to actually start first. Anyone got some tips on what I should actually do first.
For context, this is supposed to be a sci-fi type alleyway with people and cars going down along, yes it doesn't look like much but I've been putting it off for the past week because I don't know what to do.