I suggest taking your time when you implement the first version of your API. Nothing is worst than developing based on a rushed v1 API, which later gets modified without you knowing. No one wants to be caught calling a deprecated function that then gets removed.

Furthermore, try to keep all of your API libraries up-to-date. For example, I was almost driven crazy by Google's v1.0 Python Spreadsheet library's lack of support for insertion based on case-sensitive row names (See http://code.google.com/apis/spreadsheets/data/1.0/developers...). There is no documentation regarding the requirement that the row name must contain only lower case characters. The .NET library is v3.0 and appears to offer much greater support for this type of basic functionality.