Honestly, the only two people in town you should care about befriending are
Daryl, Nina, and Flora. They are the only two that will give you anything
worthwhile once you are friends. But, if you just want to be friendly, more
power to you.
Loved Item/Liked Item/So-So Item/Disliked Item/Hated Item
First-gift FP scale: +9 / +3 / +1 / -3 / -9
Extra-gift FP scale: +3 / +1 / 0 / -3 / -9
This means that if you give a person an item that they really love, and it
raises their FP by 9, giving them another of the same item on the same day
will only raise it by 3 more each time.
If you give them an item that they like and it raises the FP by 3, giving
them more on the same day will raise the FP by 1 each time.
If you give them a so-so gift, it will raise the FP by 1, and more of those
gifts on the same day will not change the FP.
If you give them a gift they dislike, it will lower the FP by 3, and more of
that gift on the same day will also lower the FP by 3.
If you give them a gift they hate, it will lower the FP by 9, and more of
that gift on the same day will also lower the FP by 9.
They also work with each other. Say you give a person a hated gift and their
FP drops by 9. If you then give them a gift they love on the same day, it
will only raise the FP by 3, because the game considers it an extra gift.
You can see everyone's FP for you by using the Love Bangle from the Sprite
Shop.
So, for making friends with Flora and Nina, both like for you to show them
your pets (will give +1 FP an unlimited number of times in a row.) If you
want to actually give them gifts, both Nina and Flora conveniently love
diamonds from the mine (they only sell for 100G each, so if you find them,
why not give them some at +9 FP each?) Be careful of giving Flora other
things from the mine - she will be insulted and her FP will drop. Nina likes
colored grasses too (just +3 FP.)
List of liked items for other villagers coming soon!