using the histogram for proper exposure

[The_Traveler]

Understanding Histograms
Expose Right

These two references above can help a lot.

The histogram does NOT tell you what is correctly exposed. It only tells you the proportion of pixels at each level of exposure.
Out in the bright daytime in a city environment, I shoot raw and routinely overexpose by 2/3 stop because I know that the sensor is getting bombarded with sky light and thus the 'normal' exposure would be underexposed in the image.
If there are lots of dark-skinned people, I compensate even more.
In many street shooting situations, I have to let the sky go to white in order to get faces exposed correctly.