(1) This wiki is hungry for natural sands and information on the processes that produced them. Avoid sampling sites affected by human activities.
(2) A handful of sand (e.g., a film canister) is enough.
(3) Take a (preferably horizontally-oriented) picture showing the sampling site in the foreground and the horizon in the background.
(4) Note the detailed location, composition, depositional system, process, provenance, and date; GPS-coordinates are helpful but not required.
(5) Process the sample. Examine the dry sample using the handlens and under a binocular microscope. Take a close-up photograph (many modern digital cameras have ultra-makro-modes allowing only ca. 2 cm distance), and don't forget a scale. This will mostly yield information on texture, but not on mineralogy; therefore, if possible, add descriptions of thin-sections and any additional information you may have.
(6) Think about the appropriate keywords and add the sample to the database.