Once you do the basic color improvements, here's what you do:
- Create a new Channel Mixer Adjustment layer (Layer>New Adjustment Layer>Channel Mixer).
- Then click to check the box that says Monochrome to make the picture black and white (but don't click OK yet).
- You may want to adjust the weights of each color in the black white configuration depending on the picture, then when it looks good to you click OK.
- Then make a duplicate of your first layer (the layer containing the picture, not the adjustment layer), make sure you have the right layer selected when you try to make the duplicate. (Layer>Duplicate Layer).
- Then move the duplicate layer above the channel mixer layer by clicking on it and dragging it.
- Then while you still have that layer selected, change it's mode from Normal to Overlay.
After you made those changes your layers should look something like this.
Your picture should now look like its somewhere between color and black and white. If it looks a little too intense try downing the opacity on the top layer a little bit to let more of the black and white through.