To get this kind of effect, simply crank down the aperture on your lens (I used F/18 here) and then adjust your shutter speed to get it suitably dark (I used 1/1000th sec). It’s that easy!
Both of my Spooky photos were taken on very pleasant days, yet they have a dark, forboding look to them. Learning to do things like this by using my camera’s controls is really fun! Give it a try.