The diving method can be done a couple different ways, but I have found this to be the most reliable, personally.
Start by equipping your wetsuit, then if you have a timer, keep it in your inventory and separate your cash into amounts of 100 bells each to fill up the rest of your bag--these will be easy to put away when you are done. If you have full letter slots, villagers cannot ask you to deliver letters or bury a time capsule, so keeping them that way can give you better chances of them asking for Public Works Projects as well. Go to the bottom leftmost or bottom rightmost point of the beach in your town, whichever you prefer, and set the timer for 5 minutes, or check your clock for an approximate timing if you don't have the timer tool. Jump into the water and swim to the corner of the map to wait for the five minutes to be up. When you get back to land, run past your villagers--one of them should ping and they just might have a PWP suggestion! Rinse and repeat~
Keep in mind that certain projects of course can only be obtained from specific personality types in villagers, so if you're after a particular Public Works Project, you might want to look into what personality would suggest it and aim to run past that type first when you get out of the water.
