Things to Keep in Mind
Friendship Level: Friendship level is a reflection of a character's fondness towards you, and is measured in friendship points (FP). You can see the amount of friendship points a certain character has with you by checking your desk in your house. You'll need to raise your friendship with characters to see certain sub-events, so it's important to raise their friendship levels whenever you get the chance. Give gifts, talk to them; even the little dialogue with the H. Goddess at the beginning of the game will raise some characters FP automatically.
Time Frame: Sub-events are only able to be completed between a certain time frame of days during the year. If you aren't able to complete a required sub-event during it's available time frame, you may fail the event path. Most sub-events only occur during clear or cloudy weather.
Requirements: You'll notice that every sub-event listed on this page has a requirements line. Some sub-events won't really have any requirements to experience it, but many require a character to be at a certain friendship level or for you to have some specific item(s) with you.
Required/Non-required Events: As you can see from the color-coded boxes above, some of the sub-events in each path are required to complete the event, and some are not. You do not have to see the non-required (light green) sub-events, but they do offer an opportunity to raise a character's friendship level and develop the story of that event some more. The blue colored sub-events are ones that occur in year 3, after you've already saved Leaf Valley.
Saving your game: When playing through all these events, you might realize you missed an event after it's too late. Luckily, the game has many save files you can utilize. It would be a good idea to save your game often and on multiple save file slots so you can always have a back-up from a few days/weeks ago.