
A lack of contrast will make your picture look hazy and flat. This histogram, for example, has no shadows or highlights and would have no depth.
I will conclude with an example of what your histogram should look like if exposure and contrast are correct.

Defined spikes of some colours, no overwhelming shadows or highlights and a full spectral range.
This concludes, I hope this simplfied look at histograms will help you understand and use them more.
~ Cof ~
About the author:
I live in Northern Ireland, currently still in school studying to do Sonic Arts at university. Enjoy photography (Nikon D70) and Photoshop (Cs), aswell as playing bass in jazz bands and singing choral/classical works.
Check out my Profile/Gallery for more tutorials and to see my work.