Not a bad first attempt...dealing with lights and shadows is one of the most challenging things (just like live film and theatre). I've found the best way to get decent, consistent daylight shadows is to get a shot from far above (where you think the sun would be coming from) then create a distant light using the "Apply Active Viewpoint Transforms" for whatever camera you're looking through - call it "Sun" or something like that - then under "Parameters," choose "Shadow Type>Raytraced" with the 3Delight render option. (You can also use "Deep Shadow Map" if you don't want to wait all day for the scene to render, but the results are less satisfactory.) Also, you will never get good shadows with a sky dome prop. Get rid of it or hide it and use some kind of sky image for your backdrop (the mountains and plants in the foreground can stay, however). I also find that free models like the Hudsons (or Lockheed Electras?) in your scene are almost never scaled properly to figures. I usually place a "dummy figure" in the scene when I import these props, place it in the doorway or a seat and just fiddle with the scale until it looks right. Hope this helps!

A good start and very nice background. The only thing i'd echo is the the scale needs a bit of work as the figures are way to big. Keep at it though :)

The Lockheeds look pretty good...