There are a number of web resources with advice on plant collecting. An annotated list is presented below.
Jacobs, B. A series of pages that discuss why and how, geared to high school age students.
Western Australia Herbarium: A pdf that can be downloaded but is also easy to absorb while reading on line. It refers to a label program for collectors. We have one for the Intermountain Herbarium (thanks to Leigh Johnston of Brigham Young University). Send an email to Michael or Mary if you would like a copy.
Davis, P.B. 1961. Very practical but, in some respects, rather dated concerning regulations etc. (note that it was written in 1961).
Several more from Australia:
And for those who like videos (Also from UNE), a four part series: