Everyone is of course 100% correct in that the best thing to do is to go in "blind" and explore, learn the game naturally rather than via Wiki and Forums. However that being said, there are some things which could to be made more clear in the game. Since he is not you, here are some tips, feel free to pass these along or not!
Top 10 things I wish someone had told me before starting my first playthrough:
1. Get a silo before a coop. It's easier that way.
2. There is a training rod for sale in the fishing shop. If you're having trouble fishing, give it a whirl.
3. Don't plant way too many crops and set yourself up to have to water them for 10 hours a day, leave yourself time and energy to explore.
4. If something Terrible happens (like accidentally blowing up your most valued possessions, or losing everything of worth you own in the mines) you can exit to title or desktop and reload to restart the day.
5. Don't sell wood or stone, or other low-value basic materials like them. Even if you have more than you need currently, that'll probably change over time.
6. Watch the "Queen of Sauce" on Sundays on the TV.
7. You can purchase a calendar from the Carpenter's shop, which makes it easy to check daily. This is helpful because folks Really like when you give them gifts on their birthday.
8. Counter intuitively, if you find yourself snacking on raw fish as an energy source early as I tend to do, it's better to eat the gold star ones than the base quality ones.
9. Chests can be placed outside of the farm, which is nice if you have somewhere you visit (like say the Mines, or fishing spots) where you tend to accumulate more materials than your initial inventory can hold.
10. Read your mail! Even if you disregard it in real life there's some helpful stuff and tips that can show up in there, so it's worth actually reading.
Hope that helps! Most of all I really hope he enjoys!