Look closely at the shadows on the individual elements and on the figure overall. (Squint at the photo to see the darker and lighter tones more clearly.) Notice how each bit is totally realistic and wouldn't be out of place in a still life.
If you wanted to attempt painting something like this, you'd first have to be totally at ease painting the individual pieces of fruit and veg. Then spend time sketching to figure out what you'd use for which facial features. Then start painting. It's definitely not a "painting in a weekend" project!
Who was Arcimboldo?
Exhibition Gallery: Arcimboldo (from About.com's Guide to Art History)