I've been through this (starting at almost 0 to getting a bit of feeling for EMC design) the past year. Among all the application notes, books, webinars etc, this is what helped me the most.
First of all, do you know against which standards your products are tested? If not, that's your first goal to find out. They will provide the requirements for your product to comply to. Also talk with your intented test house, they should be able to help you understand what those standards mean in practice.
Next, find user "interference technologies" on YouTube and watch the webinars with Keith Armstrong. He does a great job explaining what is involved in EMC and design.
If you want just one book, I'd recommend Henry Ott's Electromagnetic Compatibility Engineering.
The first part explains the concepts, the second part is on applying it to your design. The third part is on testing. His book is very complete, and to my experience you can read a chapter quite separately from the others. So skip the sections that go over your head the first time.
Finally, understanding EMC and engineering for it takes a while as it is a broad subject that isn't the most intuitive imho.