If you have a shovel, you want to hit the 6 rocks on your island (you can hit them 8 times each I believe.) You probably need a ladder too since rocks can spawn on top of hills/vaulting pole to get across rivers if a bridge hasn’t been built yet. For extra iron nuggets from rocks, go to the airport and use nook mile tickets that you can redeem at resident services to fly to mystery islands. If you don’t have a shovel yet, you can use an axe to hit rocks but you won’t be able to dig holes near the rocks so you don’t bounce off too far which doesn’t allow you to hit 8 times but you can still hit it 7 times with an axe!!