Apart from enhancing the image by manipulating the color or light information in it, we can in fact, add elements just by using Photoshop.
Although this kind of "tricks" are not real (as in not calculated by the renderer), we will fake some effects. The benefits for using them are pretty big, because they can be done more quickly than by modo's renderer, and still add to the final image. Let me show you the main post-production special effects that I use.
Bloom is a lighting effect that spreads a glow around bright parts of the image. The things like an opened window, or a light bulb can show this effect. You can generate it right inside modo, but it's always interesting knowing how to fake it in Photoshop, in case you prefer the post-production option.
This is a very simple scene, just to show you the effect of the bloom trick. There you see a strong source of light, that is the floating ball. Let's fake some bloom for it.