This tutorial is quite simple but has some tricks. I made a photo of medusa and wanted to make it blueish, glowing and more unreal. (medusas are unreal creatures by themselves!)
Here is my original photo. Lets keep it as is for a while.
Create new document, fill it with blue gradient.
Add new layer, and with very large white brush, put a spot on top of picture.
Apply some blur to this layer, and change its opacity to Soft light or Overlay.
Here is the medusa photo again. I want to get rid of colors (make picture black and white) and the best way for this particular photo is copying information from a channel. Open channels tab, and select the channel that contains best black and white picture (in my case, it was Red).
Copy image (Ctrl-A, Ctrl-C) from Red channel to RGB channel. Take a look at your Layers panel - if your selected layer is Background, double-click it and rename to something else (because we will need to add transparency and it's not possible with Background layer). And that's where the trick starts! Watch the shortcuts: Ctrl-A, Ctrl-C (copy black and white image) Q, Ctrl-V, Q (paste into mask) Ctrl-Shift-I (invert selection) Del - remove selection Ctrl-U, Lightness = +100 - make all image white. What we just did? We took black/white image, and converted all black color to transparency (leaving only white).
copy this image to previously designed background.
Duplicate layer with medusa and blur it (say, 8-10 pixels).
And last step - change blend mode of layer with Medusa to Overlay, and blend mode of layer with blurred medusa to Soft Light. That's all! :-)