One of the biggest mistakes a newbie to Sketchup can make is to just use the default material textures as-is. For some things they work great but you can vastly increase the value of Sketchup's built in materials by simply tweaking the settings just a little bit, for example:
The Metal_Corrugated_Shiny texture works great for corrugated metal but if you bump up the default size from 4" x 4" to 10' x 10' you now have some pretty realistic Aluminum or chrome.
Easy Tweak, great effect, try this with other materials as well. You can often times create very realistic materials right in Sketchup without ever opening an image editing program.