Another good link
http://www.cambridgeincolour.com/tutorials.htm
and this one
http://www.ronbigelow.com/articles/articles.htm There are 3 Articles here, 1 under Equipment/Field issues and 2 under Editing/Photoshop.
The main point, at first anyway, is to make sure that the histogram has not got a peak at the extreme left or right edge as this means that detail is being recorded as pure black or pure white.
As usual it is not as simple as that! You may have some shadows where you are not interested in the detail or there may be reflected highlights, such as sunlight on water, where again you are not interested in the detail.
The idea of getting the histogram as far to the right as possible is to make use of the dynamic range of the sensor, you then use PP to get the image back to where you want it.
Ken Rockwell mentions this but he also advocates shooting JPEG, with JPEG it is not so easy to change the image a lot without degradation.
The other use of the histogram is when editing, keep looking at it when making changes to see what it is doing. You may start hitting the left or right edges or you may see a "combing" effect where there are gaps in the histogram. This shows that data has been lost and will degrade the image, this normally occurs sooner with JPEGs than raw.