Organic! Why? It means most of the ingredients will be farmed/acquired organically which makes the land happier (so, the source is better)
Fairtrade! Why? Well, if you are going the green route, then some of the ingredients are going to come from tropical sources (like coconut oil, for example) if these are fairly traded goods then thats better for the farmer at the source, and if its approved by the fairtrade guys, then it probably means they haven't torn up a load of rainforest to make way for coconut plantations! (Hopefully... :-/)
Avoid long sounding chemical names! Ok, a bit vague but lots of the chemicals in products are there for the fluff factor - bubbles in bubble bath aren't *necessary* to clean you, its just a sort of psychological hint that says "yes, look how clean you are now with all the bubbles. Mmmm, bubbles.".
Here's a good overview of some products:
http://www.theecologist.org/pages/archive_detail.asp?content_id=1168
and here some you should most definitely avoid:
http://www.theecologist.org/pages/archive_detail.asp?content_id=879
some of the ingredients are scary, I know that whatever we do seems to be bad, but this stuff is both bad and unnescessary, and a lot of it ends up in water systems (or fixes heavy metals into water systems) which is damaging to both ecosystems, and (on a selfish note) *our* bodies!