When preparing for the Step 1, try to keep in mind that the 1st year MBBS subjects create your base for future studies.
We’ve all been through that post-NEET euphoria (as our professors like to call it) when you don’t feel like returning to that hectic and strenuous routine of daily studying, and end up cutting ourselves slack in those initial few months. I’m not saying it’s a bad thing; by all means, you should enjoy every bit of your MBBS! Just try not to regret later, especially when you’re on a long journey like that of the USMLE prep.
I’d recommend you stick to standard books for your course, so that you aren’t going far from what’s needed in class while at the same time improving your understanding of each subject.
Also, start studying from Kaplan lecture notes as well as their videos. It’s best to use the latest edition, but it’s not necessary that you buy originals as it can end up being pretty expensive. What I personally did was refer to Kaplan once I was done with each unit (after it was taught in class and I had studied it from the standard books).