Many varying standards here, though most important advice I could give would be to completely abandon your entire notion of "good" vs "bad" grades.
1) Pass -- Pre-clinically these are what you need. These are good. Passing will enable you to ultimately graduate medical school.
2) Average -- we'll assume this means passing unless your class is a bunch of idiots. Average is also good. It means you will graduate. It also means you're performing on par with a crapload of other highly motivated intelligent people
3) Above-average -- still passing. This is good because you will graduate (see the pattern here?). It means that whether because of hard work or higher baseline intelligence, you are performing above the level of most of your classmates. f
4) Acing everything -- you're a badass. You will graduate. This is good.
What I tell every entering M1 which was told to me and for which I am eternally thankful:
At the beginning, you need to hit the ground running and study like you've never studied before. Treat it almost like your dedicated step 1 prep time, just minus the stress of knowing you have to take The Beast soon. Learn the material in a level of detail so obsessive that there's nothing they could ask you couldn't answer. Live and breathe school at the beginning. Do this for the first couple of exams. The grades you get on these should reflect what is possible for you when giving it your absolute best effort. This is actually the information you need, not whether something is good or bad. You need to know what your maximum is. Then:
A) if your max is 98-100 on exams, then maybe dial back the effort a tad to preserve sanity and allow time for things like research and ECs you care about. You will almost certainly be AOA. You will do well on Steps.
B) if your max is 90-ish, you have to decide if you can sustain this long term or whether you want to titrate your effort back a bit to maintain sanity and stay at or above the class average; depending on your school this may also affect AOA eligibility.
C) if your max is 80s around the class average, again, decide how sustainable it is and titrate accordingly. These are people who will probably not end up AOA. This is also the range where you may find some benefit in putting more focus on step 1 prep alongside classwork. Again, you won't know if you're in this group without a trial run of max effort.
D) if your max effort is just on the edge of passing, then you're in for a tough road. Start seeking help and refining your study methods to see if you can maintain or improve performance. This is the group of people for whom medical school is a real struggle.
F) if your max effort is below passing, then you need to seek help and see if you can pull things up or start thinking about alternative careers. Again, if you truly give your best effort and don't pass, then you know and can avoid a lot of debt by dropping early. If you phone it in a bit, you'll drag on for a couple years racking up more debt as you gradually increase your effort only to realize it isn't enough.
So abandon the notion of 'good' and instead focus on figuring out what your personal best is. Then titrate for sanity. 🙂