Hoard as many axes, flowers, saplings as you can! Once you start modeling your town, you will need a lot of these.
If you plan on putting roads with patterns, plan ahead. Rocks and houses can mess your plans fast enough... Talk to you villagers often, they might have requests for you! Talk to every NPCs too, and buy a lot from the shops on the Main Street, many upgrades require you to have spent a specific amount of bells in the shops.
Each time you catch a new fish or bug, don't sell it! Bring it to the museum! Otherwise, if you plan to fill your museum later on, good luck on finding what you are missing...