The number of images on my hard drive is spinning out of control and I never got around to using dedicated software with image tags for my images (maybe I should). Lately, I am paying more attention when naming an image file. And the one thing that helped me most is to put the noun first. For example:

• sky_sunny.jpg
• sunny_sky.jpg. 

The latter is how we are used to think, the first is best for sorting and finding things on a computer.