When working in Photoshop, make sure the Display Settings are set to the correct profiles. These will have been calibrated – preferences/display settings/UWE profile2016.
Photoshop – Edit/Colour Settings/Working Space/Europe Prepress 3. This ensures that what you are viewing on screen pretty much equates to how the image will be printed.
It is also possible to Soft Proof the image by adding a colour profile which simulates the paper stock to be printed on. You can then make a copy of the image, apply the soft proofing and then edit accordingly to achieve the most similar appearance.
When saving a jpeg for the web, 100 or 150dpi will be suitable. This means that the size of the file will be much smaller, and thus more suited for internet upload.