Use RAW if possible
I guess an early thing I
learned was to shoot Canon RAW format photos. This is a loss-less
but compressed file format that Canon has developed and is
substantially smaller than TIFF files. As such, there are no
compression artefacts or patchy pixelization that you can see with
JPEG, so consequently one less thing to worry about when processing
your files. There is also essentially no in-camera processing (such
as contrast, colour or sharpening adjustments). This gives you total
control over the final output of you shots. Great for us obsessive
control freaks :-) . The Down side - of course - is that it is
still much larger than JPEG so less shots per card. Hence my
preference for 256meg CF cards.
Use wide angle (macro)
Stop and think!