Walk around. Talk to people, go everywhere the game lets you, interact with everything that looks interactable (I couldn't figure out how to buy seeds for a whole in-game year when I started so yea). Check out the abandoned building near the fountain and the glowing thingy in it. Try to do what your journal tells you to.
If fishing is too hard dw it'll get easier as you level it up. Get a training rod at the fishing shop on the beach, it's 25 g and will make it easier immediately if you need to. Utilize zooming in and out, I didn't know you could do that and passed out at 2 am a lot.
There's nothing you specifically should be doing, because the game is best enjoyed spoilerless when you discover stuff yourself. Don't worry about doing everything not in the best or fastest way - its not punished by the game in any way, the things you can miss are very minor and make no difference.
Everything I said in the first part is prob obvious/what you're already doing. It's more important to enjoy it yourself instead of rushing everything so I'm not gonna tell you much else. Maybe someone else will.