I go out and swim from top to bottom corner and then back. Once back on land I look for everyone who is outside at the time. One of them will have something they need to tell me. If your lucky it will be them suggesting a new PWP for the time. I have heard if you make sure your pockets are full. With tools or items that can't be given to your neighbors. It will narrow the type of things they may say to you. I haven't tried it yet so I'm not sure about that part.
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If your inventory is totally full with anything, they won't try to buy, sell, or give you anything. Reason being, you need at least 1 free inventory space for any sort of transaction, even sales. It's programmed that way as a fail-safe in case a sale puts you over 99,999 and money bags need to be added to your inventory as a result. (edit: Actually, they still might try to buy furniture off you if your bells are low enough)
An easy way to fill your inventory is to just pick up a ton of flowers from one location, then when you're done getting your suggestion just put them back.
Oh, and you don't need to catch anything if you don't want to. I think the reason diving causes a "reset" has to do with jellyfishes spawning, since they might be considered NPCs. That said, dialogue still resets on its own given enough time. Using the diving trick just makes it happen faster.
edit: And make sure to initiate conversation any time they stop trying to run up to you. If they're waiting to tell you you've been playing too long, they won't run over to talk to you. Also, dig holes around the villagers to speed things up. It makes it much easier if you know where everyone is. Plus you can go after a specific villager, since only certain personalities give certain PWP suggestions.