Make sure everyone is looking at the same tree, clump of shrubs, or even an obvious building - and use a conventional clock to describe the spot. For example, 12 o'clock is the very top of the tree in front of you, and 6 o'clock is the lowest visible branches (not necessarily the ground). 3 o'clock and 9 o'clock are located as expect on the 'face' of the tree.
Clock directions can also be useful to give angles from a particular point. For example, "the bird is at 7 o'clock, about 10 feet down from the highest point on the dark green tree."
photo © adrian binns