1: The Clock
In the top left corner of the screen is a clock that shows the date, time of day and amount of time you have left before fainting. It's important that you check this thing regularly and plan ahead. The game operates on a weekly basis, with "Echoday" being a day off for most of the characters.
2: Action Limit and Restoring Energy
You can restore energy by eating food, though the primary way of regaining energy is from sleeping in beds. There are two beds you can unlock in the game, both of which are found in the early game. The one you unlock in the first area will start you out at the beginning of the next day regardless of when you went to sleep. This is especially useful for observing the routines of the townspeople, who are located nearby. The second bed is unlocked a little later into the game and will make you sleep for a full half-day, waking up when it's either day or night depending on when you went to sleep.

3: Yoshida
There's a purple bird hanging around the town square that explains the utility of items. His commentary isn't always helpful, but he's pretty useful overall.
4: Octolips
Octolips are a consumable item that you can purchase after helping this vendor in the early game.
When eaten, an octolips will instantly teleport you to whichever bed you last slept in.
5: Getting Money
Rescuing monsters rewards you with a little bit of cash, but this is an unsubstantial amount for the whole game. The only other avenue for getting money is through fishing. You can purchase a fishing rod in the first area of the game along with bait, though there is an option to get bait for free a little later down the line. There are three fishing spots in the game, though the one found in the desert area gives you the most expensive fish. Spending a full day or two up here will give you more than enough money to get through the game.
When you want to sell, return to the shop in the first area and present your fish to the shopkeeper.
6: Hager Badges
In the mid game, you are required to get a Hager Gold Badge in order to access a laboratory. This would normally require donating a lot of money, though there is a hidden quest that allows you to get the badge for free. First, you need to check the fridge of the American House in the middle of the night when the mother character leaves the room. Then, return to the starting town and show the Hager badge to the king. He will swap your badge for a gold one.
7: Quality
The game has a blur filter, which is enabled by default. You can restore the pixel-perfect look by pressing "-" on the Switch release and "L2+R2" on the PlayStation release.
8: Check the Wiki
The wacky moments you get from observing the many characters of Moon are my favourite parts of the game, though I can't deny that it can be a drag due to the large amount of dead air. The "
Moon Wiki" over on Fandom has detailed schedules for each of the characters in the game, along with hints on how to collect their love. Some of the puzzles in this game are incredibly cryptic and random, so I don't think there's any shame in looking up the solutions online.