Plastic wrap is a filter (from the Filters menu). You do not want to start using filters. Everyone knows what they look like and anyone using them is instantly branded an amatuer. You can actually create some alright stuff with filters, for example neat explosion and fire effects for spring. For wallpapers though, its just not a good idea.
The clouds show a good understanding of light and shadow, but the colours are too flat. Need more subtlety and depth. Its also suffering from airbrushyness. Its something that is a real problem with photoshop and it takes a lot of practice to not get your digital paintings just screaming the fact they were made with the photoshop airbrush.
If you want to learn how to use photoshop better, look up some tutorials. There are plenty out there, google is always a good place to start, and
CGtalk will blow your mind.