Right Speaker = [Red +][Black -] (like the speaker terminals on most speakers)

Left Speaker = [White +][Green -]

If there is no obvious left or right speaker in a ceiling i make the "first" speaker red and black. The first speaker is where the home run lands and either continues on to the "last" speaker or gets spliced to the last speaker. No real reason to do it this way other than to have a standard practice. It lets me know where my splice point is.