Technically cross processing is an effect done with certain chemicals while developing old school film, but as always it can be recreated digitally pretty easily. Using a Curves adjustment change the red and green channels to an S-shape curve, while changing the blue channel to a reversed S-shape, better explained here Cross Process. While doing some research I really liked the “Cross Process” effect with something called, “high clarity”, I found here High Clarity. Don’t follow these exactly, you will need to vary the setting based on the photo you are using, due to different colors, and overall lighting.
After I put these two together I got something I thought look pretty good.
I also found a free download called “light leaks” – light leaks – that are some pretty cool stock images that you can screen over photos. Something I tried quickly –