Summertime Saga is segregated into days which contain three time slots - morning, daytime, and evening. All of these time periods will allow you to do different things and most goals need to be completed within a time limit so sleeping unnecessarily can skip your whole day and waste a bunch of time.
Even in the evening when it can be hard to find something to do you can participate in rap battles or play on your computer to help raise your stats. 

More often than not the answer to your question may be hidden in the dialogue. If you're stuck on what to do go back and talk to the character again and they may give you a hint of where you should be looking or what you have to do.

Not only is one of your main overarching goals to save money for college but you also need to make money to complete tonnes of quest lines within the game.
Often you'll need to have a spare few hundred dollars to buy a gift for a friend or an item you might need in order to move the story further.

As a bonus playing the mini-games to make money can help you further quest lines with the characters you work for. 

Your stats are essential for progressing questlines as well as doing well at school and leveling them up as soon as possible will mean you don't have to backtrack as much throughout the game.
If a quest has red a check in the text like [STR] this means you need to improve that stat more before you can continue. 

From Day 1 you will have access to Dianne's house to help her clean her garden and earn money. You can play this game any time during the day and will take up one time slot. It will also help you to move forward her storyline.
This game is quite simple and just has you selecting the items she wants removed from her garden within the time limit. Some of the items are obvious like prickly weeds and spiders but also round fruits and vegetables are also undesirable.
The amount of items you need to remove seems to be random. The more items you remove the more money you can earn and if you get rid of all the unwanted items the game will automatically finish stopping the timer. Usually, you can earn around $100 from this mini-game.

In Summertime Saga you will need to make money to purchase various items from characters or by going to the Mall that are needed to complete quests.
There are two ways to earn money and both require completing mini-games for your chance to earn cash.

After Day 1 you can find a pizza advertisement in your letterbox which will open Tony's Pizza The Pizzeria as a location on your map. 
Go to the Pizzeria and talk to Tony about becoming a delivery boy and he'll tell you to come back later. Return the next day to talk to him again.
This time Tony will tell you to get a bicycle or something and to just take the pizzas off the counter to start your delivery.


To get a bicycle you'll need to purchase one from Consum-R at the Mall for $500.
Once you have the bicycle head back and select the pizzas on the counter to start the mini-game.
The mini-game has you riding along a path on a 2D plane as houses appear, some of which will have pizza slices above them. On the bottom right-hand side of the screen you have three pizzas and you need to select the pizza that matches the slice above a house.
The timing on this is tricky and you need to click on the pizza just as your bicycle is at the beginning of the house. Playing this game is harder than gardening but can easily net you much more money per delivery session.