* Read the summary of changes in Python 3: http://docs.python.org/release/3.0.1/whatsnew/3.0.html

* See Guido Rossum's Transitional Development notes here: http://www.artima.com/weblogs/viewpost.jsp?thread=208549

* Read Mark Pilgrim's excellent chapter from Dive into Python 3: http://diveintopython3.org/porting-code-to-python-3-with-2to...

* Use Python 2.7 and turn on deprecation warnings.

EDIT: Found this great guide to forward compatibility:

* http://www.slideshare.net/regebro/python-3-compatibility-pyc...