If your converting an image from colour to GS in photoshop it will often go very flat and lack any contrast, once it's converted in PS open your levels (cmd alt L), if your not familiar with this screen you'll see a histogram, a graphic chart representing the tonal info in the image, it's a bit trial and error but you might find dragging the small left hand arrow (at the bottom of the histogram) to the right, it will darken the dark areas and create a punchier image. Save the file as .psd or .jpg and place if in Indesign then select 'adobe pdf preset' - 'press quality'. Lastly and most importantly when you send the resulting pdf to the printers instruct them to only print black, if printers can get it wrong they will.
Hope that helps