I was asked an interesting question today. One I admit I've never really thought about too much. The question was this: if you haven't seen the moon for a few months and then suddenly you had a clear night and saw a quarter moon in the sky, could you tell if it was waxing or waning?
(Waxing means going from a new moon to a full moon, waning means the opposite).
The answer is actually very simple if you like those rule of thumb things but he doesn't want to know the answer right yet because he wants to see what other people say. So I won't give the answer here, or at least not in this post. If you feel like commenting with your answer though, feel free!
Although the answer is simple it depends whether you're in the northern or southern hemisphere and you're a little stuffed if you live on or near the equator! So I think I have a general answer as well which should work no matter where you are. I'm sure this is in Google somewhere but I promise I haven't looked (yet!). You need to know west from east, though, or at least where the sun sets or where it rises with respect to your location.
As for the above shot (with some nice earthshine), it was taken just after sunset from home looking roughly to the west. Is it a waxing or waning moon? You have enough information to answer the question!