If you have a free summer, don't worry too much about step 1 prep - if you want to flip through first aid and review topics like biochem or physio that's fine. Once you start your second year, focus on learning the class material well and supplement your coursework with popular board study resources such as pathoma, first aid, and sketchymedical; if you would like, also consider purchasing access to a question bank like USMLE Rx, Kaplan, and/or UWorld (though most people save this one for the dedicated study period) to reinforce concepts. By the time you hit the dedicated study period, most things should feel familiar to you, save for some first year topics like biochem. During this time, most people use pathoma, first aid, and question banks to review for the boards.
Some people sell out to studying for boards instead of aiming to do well in class, but I personally wouldn't recommend this. It should be possible to prepare for boards and do well in class if you're focused.
