Begin with this introduction to fieldwork methodology for advice on how to prepare for and begin your fieldwork, what to do once you're in the field, how to process, store, and analyze your data, and more.
(See some of the guides to the right for more linguistics-oriented information.)
The classic guide to writing fieldnotes. An earlier edition is also available.
Linguistics-specific guides to fieldwork (on reserve in Magill Library or online):