The following image of the Muir Trail did a great job of capturing the environment, but the colors were a little flat. For our purposes, we wanted to evoke the feeling of a vintage postcard. Regardless of the image, the process for me is relatively the same. My go-to adjustments are: gradient maps, color balance, hue/saturation and curves.
A gradient map will help you reassign dark and light values in your image. In this example, my blacks are dark blue and my whites are a pale brown. I used color balance to do minor color adjustments to the image as a whole — a little can go a long way here. Hue/saturation will let you drill down to specific colors. In this case, I used this adjustment to turn my blues into teal and desaturate my greens. Lastly, I use curves to exaggerate my contrast.
For the image of poker player Maria Ho, the workflow was identical. The image as a whole was desaturated and the contrast was boosted to give it a moody feel. The tones were mapped to gold and purple to give the image a dark and high-end feel. As mentioned before, the process is the same, but the outcome is noticeably different.
The last example is an image of a trolley in San Diego. The image has an awesome perspective, but it's drowned in dark tones. The dark blues carry more weight than the red values of the trolley. To remedy this, the exposure was increased using curves, making the sky a much lighter shade of blue (the clouds were added in post), and then hue and saturation was used to really make the emphasis the red. In the original image if you asked the view which color they saw first, the most likely responses would be either red or blue. In the corrected image, most people will see the red first — really driving home the story of the Trolley in this image.