This is the way I do things, it doesn't make it the best way, it is just my way :)
* Print sizes aren't just sizes but they are different shapes too.
* Your print lab will tell you what ppi your image needs to be at to print properly. My print lab suggests 300ppi.
*Your images do not come out of your camera an 8x10 so you will have to crop for print.
This is how I do things:
Have my edited images in a folder, once my client makes their print order I gather the files they want to print and make a copy of them then put them into their own folder labeled print.
I then go into Photoshop and select my crop tool, print size changed to the correct one and resolution at 300 pixels per inch (ppi). Then I crop making sure to keep the composition as I intended.
I NEVER crop an already cropped image. I always go back to the uncropped version, again because they aren't just different sizes, but different shapes too.
Cropping from a cropped image will cause you to begin to lose your composition, and potentially start to lose important parts of your image such as the top of heads or other body parts.
Information straight from WHCC- a professional print lab:Q. I just couldn't seem to get the files to 8x10's without distorting the picture.
A. When your original file size is not the same aspect ratio as an 8x10 the image will distort when you use image size in Photoshop with your constrain proportions unchecked to size the file. You can crop you file one of two ways to get the file to an 8x10 size for test prints: 1-use the cropping tool in Photoshop to size the file to 8x10 at 300 ppi. However, you will lose some of your image. Or, you can go to image size check the constrain proportions box, size your file to the closest it can be to 8x10 but size under not over. Then take your 7.5x10 file (for example) go under image scroll down to canvas size and canvas the file up to 8x10. This way you will have a file size at 8x10 without cropping or losing any of the image. The canvassing method can also be use for printing a custom sized print with us. If you are cropping your files in Lightroom this should be done from the Develop screen by setting your file dimensions and then dragging the crop tool over your image.
Edit to add:
When I edit my images I do not crop them at all.
For images on CD I do not crop at all since I do not know what size my clients will want to print.