Are there any special parameters when placing JPGs on an artboard

I am using Illustrator CC on Windows 10. I am working on large project where I am placing JPGs on an A1 artboard. In several instances it appears as though once the images are placed on the artboard they are not as sharp as the original JPG. I will ultamitally export the art boards to TIF files for printing.

1. Does Illustrator do anything to a JPG that I should be aware of? 

2. Should I be linking to Tiff to start with?

3. Is there anything I should know that is unique about placing an image on the art board?

This is really important right now. I am about a week into the project and I have two weeks to go. If there is anything I should be taking intoconsideration, I need to know it now.

Thank you in advance. I really look forward to your feedback,

Jim