What procedures are followed for a planned landing in a field?
Not just helicopters. It happens all the time in my neck of the woods (Alaska) in small planes with big bouncy tires. We probably have more "field landings" (called bush landings, or "off airport operations") than landings at actual airports. OK, well maybe not quite that many - but enough that my local aviation college has an entire semester course dedicated to it for it's professional piloting program.

The first act is usually a low pass to inspect the conditions and determine the best landing direction (if there is more than one option), assuming that the winds will allow it. If there are other aircraft in the area, which sometimes happens at popular hunting/fishing/floating drop-off locations or glacier tours, then self-announcing on frequency is done like at a non-towered airport.  But, it's usually remote enough that it's not done. 

Quite frequently, it's two planes for one party's charter - one to carry the people, and one to carry their gear. In that case, they're usually talking to each other the whole way, and know each other's intentions anyway.