Helpful hints for photographing plants
Lens focal length - wide-angle, normal, telephoto
Depth of field - using f stops to get more of your photo in sharp focus
Exposure - managing the light
Composing the picture - what are you trying to show ?
Lighting - using natural light
Lighting with flash - different types of flash set-ups for botanical photography
Why use flash? and what sort of equipment is available.
A quick and cheap in-built flash technique for plant photos for SLRs with macro lens
Many of the photos in the APII photograph collection were taken by Murray Fagg. This link takes you to a web page describing his do-it-yourself flash setup using the camera's own pop-up flash. It also includes example of photos taken using this set-up.