The method I use seems to be the most effective when getting PWP suggestions, so I'll share it.
First off, I find all villagers that are outside to see who they are. There can only be up to five villagers outside at a time and that's usually how many are out there, so if you only find like three or four, chances are there are still others out there. Using the megaphone helps, which I will also mention later. Then what I do is I "trap" those villagers who are outside, so I know where they are. You do this by digging holes with your shovel around them so they can't move around (sounds awful I know lol but it helps). If you don't want to do this, then keep your megaphone on hand and call their names if you can't find them later on. Next, make sure you have your swimsuit on obviously. Also make sure you have a timer. Then, fill all your pockets with flowers. You can have your tools, but make sure you have no empty slots or any items because villagers always ask to buy/trade/sell/give items. Now, you can start with the actual diving part. Set your timer for
3 minutes (I know other people have said 5 minutes, but for me it works with 3. Those 2 minutes help a lot). Go into the ocean and wait until the timer is done. You don't have to swim around, usually what I do is just set my 3DS to the side and do something else like watch YouTube or something. Once the timer is done, walk around all the villagers who are outside and see who pings. 95% of the time, someone should ping. If someone doesn't ping, it might be because they need to say the "take a break" or whatever. They do this
every one hour. If nobody says that and nobody is pinging, just do the trick again.
I hope this helps, this works for me.
Doing the diving trick takes a long time, sometimes even two hours at a time, so be prepared. That's why I always do something else during this.
