In Photoshop, you can change a layers Blend Mode to create interesting effects. You can also use the Layers Styles Panel to access the more advanced blending options such as the Blend If sliders. The advanced blending option give you even more control over your effects. Watch how they work.
For more tips like this, be sure to check out my series on Skillfeed.
Update: As of October 2015, Skillfeed no longer hosts training videos.