After you rest on your cot in your tent, your first day begins, and time on your island will match real world time. Here is some advice for things to do on your first day.
Check your Mail
If your mailbox outside of your tent is flashing, be sure to check it.
Use your NookPhone
Your NookPhone has many helpful features. You will use it a lot, so take some time to look at all of its features.
DIY allows you to craft things like tools, furniture, and so on. To unlock DIY, talk to Tom Nook in the Resident Services Tent and ask for a DIY presentation. Afterward, Tom Nook gives you some free recipes. You can use the workbench in the tent to build more things. For example, you can build your own tools.
After unlocking the DIY app, if you have a recipe card in your inventory, use the recipe card to learn the recipe.
You can gather things like shells, weeds, fruits, and other things, and sell them to Timmy in the Resident Services Tent to earn some bells. You can use the bells to buy your first tools from Timmy, which will help you earn even more bells. You might not want to sell all the weeds yet because you can use them later to earn miles.
You can build your own tools, or you can buy them from Timmy with Bells.
Replace Broken Tools
Tools will break after you have used them a certain number of times. Flimsy tools don't last very long, so you might want to purchase them with bells, instead of using materials to keep building them.
Earn Miles, and Pay Off Tom Nook
It's important to pay off Tom Nook as soon as possible, because new features are unlocked when you do. Use the Nook Miles App on your Nook Phone to look for ways to earn miles. If you have earned miles, open the Nook Miles App, and you can use the right control stick to quickly jump to the task that you completed, to claim the miles from it.
Upgrade to a House
Once you pay Tom Nook 5000 miles, ask him to upgrade your tent to a house. Your house will be built at 5AM. This will unlock Nook Miles+, which makes it even easier to earn miles, and allows you to redeem your miles for a wider range of things.
Check Your Nook Miles App
After you choose to upgrade to a house, your Nook Miles App is upgraded, giving you easier ways to earn Nook Miles.
Redeem Miles for Upgrades
In the Resident Services Tent, there is a Nook Stop terminal that you can use to deposit bells, buy rare items from the Nook Shop, and redeem Nook Miles. After you pay off Tom Nook and ask him to upgrade your tent to a house, use the Redeem Miles feature of the Nook Stop terminal to get upgrades such as a larger inventory, a Tool Ring to make it easier to switch tools, an upgrade to the Custom Designs App, and more.
Give Creatures to Tom Nook
When you talk to Tom Nook, he gives you the option to donate bugs and fish. Give him unique bugs and fish that you haven't given him before. After you give him one creature, he adds the Critterpedia App to your NookPhone, which will record information about bugs and fish that you have caught before. After donating some creatures, he gives you more recipes, including an axe recipe, and after donating more creatures, he gives you flower seeds, and a watering can recipe. After more creatures, he calls Blathers, and then he gives you a Blathers Tent Marker.
Build Blathers's Tent
After you have given five creatures to Tom Nook and gotten the Blathers Tent Marker, be sure to build it in your town. There are many things that are only unlocked after Blathers's tent is built.
Place Other Bugs Outside
After you have given five donations to Tom Nook, he won't accept donations anymore, so you can sell bugs and fish to Timmy, but you should keep the bugs and fish that you haven't caught before, so that you can give them to Blathers when he arrives. You don't have much room in your tent, though, so you should place them outside for now.