This regularly happens round our way. There have been a few massive planning proposals and the Residents' Association (or sometimes just a group of neighbours) sends out leaflets outlining the proposal, the potential effects, how to register an objection, and suggestions of what to say in an objection.
You can also go round with a petition for people to sign (many people ignore leaflets posted through their door or cba to write a letter, but are happy to sign a petition.)
Sometimes residents even put up posters in their front gardens or set up a website.
The local council has a track record of approving bonkers applications, and also a track record of failing to inform residents about applications near them. So people have started doing all this stuff. There are a few residents who regularly check the council website and put the word out. It's the only way most people even hear about giant planning proposals before the diggers turn up on their street, so they're normally quite grateful!
It's crazy that people need to go that far, but after seeing some of the building projects here I can see their point. We're not just talking about someone's conservatory... more like random tower blocks parked in the middle of streets of little semis.
You do need to keep it all factual and not defamatory, though, obviously.