My advice, honestly?
RELAX.
Enjoy your first year, because it'll be the chillest by far. And seriously, I can't count the number of people I know who were ultra-mega-gunners as M1s, who were dead set on matching neurosurg or ortho or plastics or ophtho. Then they hit M3 and discover they totally love something completely different. Then it's kinda awkward because they suddenly have to explain why they're doing X instead of Y, and let a bunch of people down, etc etc.
In a way, I was the same; I thought maybe I'd do cardiology or something, and I shadowed. Didn't bust my ass to really gun it up, but in retrospect I'm really glad I didn't -- because I realized in the first rotation of third year that I hated, hated, hated inpatient work. I also hated the unholy trinities of HTN/AMI/CHF and HTN/diabetes/hyperlipidemia, which you basically can't get away from if you do any sort of adult inpatient medicine. Fortunately, halfway through the year I discovered ophtho -- basically by whim and by luck -- and found my true home. I was a bit nervous about getting my ass in gear and applying for ophtho in essentially 6 months, but in the end it worked out fine. Well, I hope it did -- I'll let you know next week 😉
But I guess my point is: ultimately, shadowing and research and showing up to grand rounds won't really tell you whether or not you REALLY like the specialty. Nothing will tell you that except doing it. And if you commit too early to something and then discover you hate it, you'll have to backtrack.
At the same time, face time with the attendings might possibly help you make a good impression? But more likely they'll just see you as a tagalong until you actually rotate with them and show them your chops. True, in the end, maybe a letter that says "X has been shadowing me since M1 and is the best damn student I've ever seen!" will sound a bit stronger than "X is the best damn student I've ever seen!" -- but imho, it's only stronger by a LITTLE. And you're weighing that small gain against the risk of having to disappoint people if/when you change your mind.
All that said, the best thing you can do for yourself in terms of future career is to ace Step 1. That doesn't mean start studying now. Depending on how you learn, that might not even mean studying throughout 2nd year. But it does mean setting aside whatever time you think you need to do well. You don't need a 260 -- but 240 really is kind of the magic number where every specialty is open to you, and you don't have to compensate for a "low" score. Once you have that in the bag, the future really starts looking wide open.