Always make adjustments to a COPY of the original image, so as not to ruin
it.  Straighten and crop first, other adjustments next, and unsharp mask
last.  Do NOT limit yourself to the auto adjustments... far better to learn
how to use the non-auto adjustments first: gamma, contrast, brightness,
saturation, etc.  If the final version needs to be downsized for some
particular use, follow that with another round of light unsharp masking to
restore sharpness.  Never over-sharpen... in fact often it is best to
sharpen only within a selected important area.

Auto modes might clip highlights and shadows, so I feel it
is best to do all operations manually.  Lean which tools are
additive but should be multiplicative (like adjust contrast)
and do not use them.  See:

 Digital Workflow
http://www.clarkvision.com/photoinfo/digitalworkflow

Roger

   Whatever you do, crop last!  Different print papers have different
format ratios and you don't want to have to create pixels to modify an 8x10
formatted image to fit a 4x6 full-frame.  Also. I try never to change the
resolution of an image until I'm ready to print it -- and I'll always keep
the original in case I want to go back and print a different (larger) size.

   Norm

First calibrate your monitor with a hardware calibrator.

Then  would suggest you start with RAW so you  learn the basics of it
and they you may not have to do that many adjustments in CS itself.

Get a copy of the following:

Real World Camera Raw with Adobe Photoshop CS (Real World) (Paperback)
by Bruce Fraser

Real World Color Management, Second Edition (Paperback)
by Bruce Fraser, Chris Murphy, Fred Bunting

Adobe Photoshop CS One-on-One (Paperback)
by Deke McClelland (Publisher)  (this is the best teach your self CS
book I've seen and it comes with a CD with the images for the
exercises)

Calibrate your monitor.  I can't say that enough.

**********************************************************

"A combat photographer should be able to make you see the
color of blood in black and white"

                    David Douglas Duncan
                Speaking on why in Vietnam
             he worked only in black and white
     http://www.hrc.utexas.edu/exhibitions/online/ddd/

Once you open a jpg save it as a psd or tiff file. Then you can work on
it and resave as often as you need to without any additional loss. Never
save a jpg as a jpg unless it it the last final step.

The power of photoshop is in the layers, each of these adjustments should be
done as an adjustment layer.  The difference is.  When you run an
adjustment, you rearrange the information.  look at a histogram before an
after a contrast adjustment.   Learning to make contrast adjustments is
relatively easy, look at some of the tutorials at adobe, get a book or if
you really need it demonstrated, there are a number of DVD tutorials,
software cinema and others, though these can be expensive, you might want to
join some photo clubs as many of them have libraries as well as classes.