Finally, we can dig in. Let's have some fun. First, let's dig into highlights. Highlights can be overused or underused. There must be a balance in the Force. What I do is choose the part of the frame or structure in which the light would be the strongest and add a shine or glare there. I also look at light as physical — given the way it reacts to objects, it seems that way at times. Think of it as a liquid that concentrates itself along the apex of the lighted structure. It might sound a bit weird, but that's my highlight theory.
Take a look at this image. Notice the subtleties of light placed on the chassis:
The lighting on glass doesn't change drastically. It's the same principle. But due to the placement of shadow, it gives off a different feel, namely feeling more like glass/plastic than metal or any other substance:
Coloring the shadows: I can't go into much detail on this one ૼ it's really playing it by eye — but the first step is to use the magic wand and select all the same colors in the pic that you want to "shadowcolor" first. Holding down the Ctrl button and clicking each solid color on the flats layer will allow you to select the multiple solid colors. See the image below for a better idea of this. Notice the "marching ants" around the same colors:
The next step is to hide the marching ants by clicking Ctrl+H for Hide. Marching ants distract me when trying to adjust colors at times so this just works for me. Remember to Ctrl+D when completed with this process so that you can continue with your work.
Next, you want to click on the shadows layer. Even though you can't see it, the colored areas are still selected on the shadow layer. So basically, you can play with the shadows that are only in the area of the color you've selected. Get it? If not, reread, because I'm sucking at that description, LOL.
Here's my trick... what I do is I brighten the shadow layer by going into brightness/contrast (see the help or guide in your copy of the software for directions. I think it's [ image > adjustments > brightness/contrast ]...) I brighten it until is a light gray, then I go to color balance and add color based on the flats and how I want the shadows to be colored. Play it by eye and before long this will show good results. It's better than opacity at 40% in black on a new layer, trust me. Anyways, keep in mind that dark colors should have dark shadows, light colors should have light-colored shadows. Before long, you'll be a master. Finally, once I've completed this, I Ctrl+D to deselect and go back to the flats and select same colors for next area of image and so on.
Next we go to the background. I can't go into detail because the background has no standard format. I usually wing it based on what I like to see. There are too many steps to this and no clear formula. I almost "paint" my backgrounds when they're done using a combination of brushes and effects that change from piece to piece. Even the blast took a while to do, sampling different effect layers that oftentimes are tedious. However, I can give you a tip on the electric bolts, which are very simple...
Create a new layer above all the layers. Use a white airbrush at about 4px and 59% flow and just draw on the bolts. Next go to [ layer > layer style > outerglow ] and choose blue from the swatch are, then adjust the settings. I normally give it a bit of spread and play with the dials. As you play with them, you can see the effects. Keep playing with them until you get desired effect. Be sure not to make the bolts stand out too much, which usually happens when you learn a new technique and get "effect happy" like I used to all the time. :-)