One interesting technique that can add intrigue to your images is to posterize the bottom layer in Photoshop and then invert the color of its duplicate upper layer before turning it into a REVEAL ALL layer mask.
This is very effective when using images made in cemeteries. You can however leave the bottom layer un-posterized for a more subtle effect. Either way just play with the images and have some fun!
(Note: There are two images of Kathy Schubert on a recent architectural ride adjusting the helmet straps of a rider prior to the beginning of the event. The darker of the two images is not an invert color but rather a solarization. The effect is a bit more subtler and subdued than the invert color adjustment.)