Keep all lines under 75 characters or so.

Two main styles for wrapping lines with brackets:

1. Break immediately after an opening bracket. Indent four spaces.

month_names = [
    'January', 'February', 'March', 'April', 'May', 'June',
    'July', 'August', 'September', 'October', 'November', 'December']

2. Break in the middle of the list. Align with the appropriate opening bracket.

month_names = ['January', 'February', 'March', 'April',
               'May', 'June', 'July', 'August', 'September',
               'October', 'November', 'December']

This also applies to function arguments (probably the most common case).

When there are no brackets, use a backslash at the end of the line. Indent wrapped lines to a meaningful depth.

print 'The number of digits shall be at most FIVE, sillyhead.', \
      len(input), 'is RIGHT OUT.'