What's a good EKG guide/book for a 4th medical student who's not clueless about ekg's but no expert either, starting internal medicine rotations?

Great book. its called "the only EKG book you'll ever need." Don't have the author's name off hand but if you search the title you will find it. This book is far superior to the other books out there and very easy to read and comprehend. .
Learning EKGs. My favorite author and producer of teaching materials on this topic (as well as arrhythmias, acls, etc. Is ken grauer. Check out his web site at: https://www.Kg-ekgpress.Com/ for a full list of resources. He has a nice pocket size handbook of basic ECG principles for the bedside.