- Black skies with white clouds.
- Oversharpened everything, with weird little halos and creepy looking highlights.
- HDR. Ugh.
- Instagram. Ugh.
A good image will be a good image without any effects at all. Post-processing should serve to enhance and improve the image, to enhance drama that is already there, to highlight the important parts, to draw the eye in so the image can engage the viewer's mind.
A bad image, or even an uninteresting image, with a bunch of post-processing effects added to it, is still bad or uninteresting. The effects may be eye catching, the the viewer won't even see the image. Maybe that's what you want, but there's an easier way to ensure the viewer doesn't see the image -- don't show it to them!