Photoshop was not designed for spot colors, but it can be made to work. This was written to facilitate ad submissions, but you may use the concept for other projects as well.
These instructions assume you will be using the Cyan plate as a substitute for a Pantone spot color.
File > New
Width and Height in the inches of your ad size
Resolution: 300 pixels/inch
Color Mode: CMYK, 8 bit
Save your new ad as a Photoshop document (.psd) with a file name that identifies you, i.e. YourOrganization-MonthYear.psd. This is your working file.
In both the tool palette and the text palette click on the black swatch and change the CMYK percentages to C-0, M-0, Y-0, K-100 (the default is a “rich black” that uses some of all color plates/channels).
Set the other color to be cyan: C-100, M-0, Y-0, K-0
Add your text using either Black or Cyan. Remember, Cyan will be replaced by the second color which will probably be something other than Cyan. Sorry: it won't look right on your computer, but it's necessary.
Blends can be used if they go between foreground and background when one is Black and other is Cyan. You may also use drop shadow and bevel and emboss. Keep an eye on the Channels panel to make sure you don’t have anything on the Magenta and Yellow plates since these will be discarded.
Photos copied into your ad document will automatically change to CMYK with information on each plate. When the Magenta and Yellow plates are discarded, the photo will turn blue. To include grayscale photos that won’t turn blue:
Open your photo as a separate document. Change it to grayscale with an image size of 300 dpi. Remember that, if the original is at 72 dpi, the photo will shrink. You can make it smaller, but it will lose quality if you try to make it larger.
Select the image and drag it into your ad. It will be on a new layer. Please do not use Smart Objects — they make huge files and cause printing problems.
It will now show information on all 4 channels. Go to Image > Adjustments > Channel Mixer. Click the box for Monochrome in the lower left corner. Enter 60% in all 4 boxes then, with Preview checked, adjust the sliders on each channel until you get the desired result. Toggle Preview off and on to compare the new with the original.
When your ad is ready, save the original in its .psd format. Then
Go to Layer > Flatten Image
Save As > Copy > Format: Photoshop PDF
When/if asked, choose highest quality, print, and binary
(The .pdf ending will keep it next to the original alphabetically.)