A quick way of doing it (using Paintshop Pro not Photoshop
) is to open the image up, resize* it to the dimensions you need (press shift+F) then do 'Sharpen' once and then 'Clarify'** at setting 1 (or 2 but no more than 2). Working with very good images helps a LOT tho as had been said
*Using 'Smart size' option in the 'Resize' window works best imo.
**Clarify can be found in the Adjust ---> Brightness and Contrast menu