So, most importantly, understand the basic electrophysiology of the heart and the technology we use to monitor it. For a basic introduction, I would recommend purchasing and studying "Rapid interpretation of EKG's; fifth edition" by Dr. Dale Dubin. It should have a bright orange cover. It's simplistic but lays out a good base. After that, establish a systematic approach on how you read and interpret an ECG and follow it everytime. I found the process espoused by this website to be helpful. https://ecgwaves.com/topic/systematic-clinical-ecg-interpretation-review-guide/ . After that, it's all about repetition, practice and further study into the physiology of it. For practice beyond my clinical work, I like to go through books like: "EKG's for the emergency physician". That book, and ones like it, generally provide a short pt description, complaint and 12 lead printout for interpretation. In the back is a written out synopsis of what the actual diagnosis was for comparison. There's a lot to it, good luck, remember to enjoy it!