What you can do
On your own you will have very little chance of stopping an unwelcome planning application. You need the strength of numbers behind you.
The first step is to find out if you are a lone voice or genuinely reflect the views of most of the local residents. The only way to do that is to ask. Prepare a short letter setting out clearly what the threat to your area is and making it clear you are against it. Ask anyone who shares your views to contact you. Make that as easy as possible with an email address, a phone number and a postal address.
Get 200 or so photocopies made. A local print shop will do that for about £20. Go from house to house and post them through the letterboxes. Don't underestimate how long that will take. It can easily take 2 hours to deliver a 100 so don't be too ambitious. Restrict your first leaflet to your road and other ones which are obviously affected by whatever it is you are protesting about.
If you get the response you hope for try and persuade three or four of them to help you in the protest. Don't try and form a committee. Keep it informal and let people do whatever they can to help. You'll be surprised what a range of talents most roads contain. Use whoever you have.
If it's a planning application, read all the documents. They will probably be available on the council's website. If not, go to the council offices to look at them. It's best to make an appointment so the papers are ready, to save you hanging around or finding they are being used by someone else and not available at all.

Go and see the Director of Planning. Explain your concerns and ask them to tell you what is happening. They will not be able to give you a personal opinion on the merits of the application but should tell you what it is all about, the council's general policy towards such applications and what planning policies are relevant.
Don't just concentrate on the public documents. Remember, under the Freedom of Information Act you can ask to see any relevant information, including pre application correspondence between a prospective developer and the council.
If you still think what is proposed is wrong keep on rallying support. Talk to your local councillors and your MP. Contact the local press. Make sure that everyone writes to the council making their opposition known. Keep an eye out for any planning committee meeting about the issue and make sure as many people as possible attend. A room full of polite protesters concentrates councillors minds.
There's a very good book about how to organise a protest called "Not in our Backyard, How to run a protest campaign and save the neighbourhood". It's written by Antony Jay, who created "Yes Minister" and can be obtained from Amazon or directly from the publishers White Ladder Press, Great Ambrook, Near Ipplepen, Devon, TQ12 5UL website www.whiteladderpress.com. Cover price £7.99.