Physiology is one of the most important subjects for USMLE Step 1. Without physiology, you wouldn't understand the pathology properly. Now, Physiology is all about concepts, which means there is less memorization. And the board loves conceptual questions so make sure you know your physiology well. Preparation for the physiology depends on what stage you are at. If you are really weak, new to physiology or still doing your basic sciences, then you must use Dr. Najeeb's Videos or Costanzo's Physiology.
Now, Dr. Najeeb is the best physiology teacher out there. So grab a copy of his physiology videos and watch them all. He draws everything on the board and make it interesting. However, his videos are long and take forever, which is why I said you should watch him if you are a beginner for physiology and have enough time to spend. I watched his videos, and it took me about 5 to 6 days to finish up. I also read the Costanzo's Physiology book during my basic sciences. I did not read the entire book, only read the systems that are in First Aid. Costanzo's Physiology is also one of the best physiology books out there and my favorite. If you plan to read it make sure you watch Dr. Najeeb with it, as he will help you to visualize many concepts from the book.
Once you are done with the Dr. Najeeb's video or Costanzo's Physiology, you can now start with the USMLE World and First Aid. Make sure you do the UW in a system wise so that you can take notes on the First Aid easily. Read every single question carefully and write down the important notes on FA. After you are done with the UW, you should be ready for any physiology questions. Trust me, UW will teach you everything that you need to know for physiology.
Here is My Recipe For Physiology:
Now, I know some of you don't like to watch videos, and you are more of a reader and want a good source to prepare for physiology. So here are two other methods that you can use:
Kaplan Physiology Lecture Notes
First Aid (optional)
First Aid (Optional)