One thing I have been doing a lot lately is to export multiple images of the same view then combining them in photoshop later taking advantage of the power of layers. What I mean by multiple images is exporting the same shot in a variety of different styles. For example I often will export a shaded with textured image without edges. Then I'll export a hidden line image. What this allows me to do then is control which edges I want to see in the finished rendering and I can control their intensity. I've also done the same thing with shadows. You can also then apply filters to portions of your images as necessary. Often I'll add noise to soften the image as a whole or to emphasize the texture of a rough surface.
I think the key to generating a good rendering straight from sketchup is to start with good material maps. Take the time to ensure that they are scaled correctly and ensure they tile in a way that isn't obvious. Take a moment and pay attention to the small details like door knobs, or other things that are easy to forget but make a world of difference.
Depending on your desired level of rendering I would suggest that you take a look at the people, cars, and trees in your model. These can be too cartoony at times and such entourage elements might actually kill a good rendering. Sometimes a bit of post processing is all that's required. Try this link http://www.howardmodels.com/digital-content/index.html for some great skies, and trees. What I do is let sketchup render the shadows of a component tree. Then in photoshop place on of these real ones over the sketchup tree. The shadows will be a bit off but they'll be close enough. Be sure when inserting entourage elements into your model either via components or in photoshop to ensure that they are lit in the same way your model is.
If you want an easy "photoreal" rendering program to work with Sketchup I recommend podium. Its great for adding light and reflections directly within sketchup itself.