I've got a great idea for a new Stack Exchange site.
How can I make my proposal on Area 51 successful?
Related: How can I propose a new site?
Get your audience right. Area 51 does not supply the built-in audience needed to create a community for you; it's up to you to bring in an audience.
A proposal on Area 51 deliberately includes only three things:
A great site has an obvious and active audience.
Don't propose a site if you can't tell us who it's for.
Please don't give me another site like this:
A site for people who are interested in coffee tables.
How do we know that there are such people? Am I one of them? This is a weak proposal and won't succeed. How do I know it won't succeed? Because you haven't told us who will go there.
The audience field is called audience and not description for a reason.
Tell me about your site for pilots, your site for dermatologists, or your site for people who play in fantasy baseball leagues, and I'll understand that you've got a real audience in mind.
Tell me about your site for "people who are interested in surreal art" and I won't be so sure.
Additionally, make sure that your audience actually shows up to vote, and has a high interest in the site, to ensure that your proposal meets the 4-month deadline for the Definition and Commitment phases.
Get the scope right.
(too small) ↑ Formulas in Google Spreadsheets | Google Spreadsheets | Google Documents | Web-based Applications | Software | Computers and Internet | Technology | The World We Live In ↓ Anything with a question mark (too large)
A site which is too small runs out of interesting questions, and fails to attract a community of interested people. Almost nobody cares enough about garlic to make a career out of it, so a site about garlic won't attract a soul.
A site which is too large fails to get answers to specific questions because the audience cannot include an expert in every possible topic.
The perfect-sized Stack Exchange site has an audience that is the perfect size for the domain. It's simple math: if you want to get answers to questions within 10 minutes, somebody who knows the answer has to log on within 10 minutes. That means that the domain of the site has to be restricted enough, or the audience large enough, to insure that questions get answers.
Sometimes on Area 51 you'll see multiple proposals where one proposal is an obvious subset of another.
Example: Gardening vs. Organic Gardening
Sometimes, the moderators on Area 51 will use their discretion to close the proposal that they think is wrongly-scope.
But you can help, too. Follow the proposal that you think has the right scope. If you think we're going to get enough gardeners to answer all gardening questions, Organic Gardening may be too small. Follow the gardening proposal. On the other hand, if you think that organic gardeners are their own community with enough of their own problems and they won't want to be relegated to an organic tag, follow the organic gardening proposal.
In either case, we'll pay attention to which of the competing proposals has the most support to decide how to build appropriately-scoped sites.
Pick the right example questions.
You're not supposed to vote on every single question to decide if it's on- or off-topic. You're also not supposed to generate hundreds of possible questions during the proposal phase -- that serves no purpose.
You're supposed to be honing in on a small number (5 to 10) of questions which exemplify the site.
A site for dogs? Golden Retrievers are on-topic. Wolves: Off topic. Barely, but off topic.
Dalmations? Obviously on topic. And this question adds nothing. We've established that Goldens are on topic. Do we really need to enumerate the breeds to understand what it means to be a site about dogs? No.
More interestingly... are we going to have medical questions about dogs? Training questions?
Look for a small number of questions which illustrate exactly what kind of questions belong here.
Think about the next phase... the commitment phase. In the commitment phase, you're going out to the dog experts to get them to commit to participate in your site. And when they ask, "what's the site about?" we're going to show them the top 10 on-topic questions and the top 10 off-topic questions so that they get it. So make your vote count, and vote for questions which are paradigmatic and which help people understand the site.
Get the topic right.
Topic names should be generic and boring.
"Psychology." (For practicing psychologists). Not "Psych Me Out!" At this stage we don't need "clever." That will come later, when the community has come together. At this stage the most important thing to do is get people together that are interested in the same site. We want to help people find each other, so use the most generic term you can think of.
Make sure your proposal appeals to high-rep SO users.
"Tell me about your site for pilots who are also professional programmers, your site for dermatologists who also deploy massive web apps, or your site for people who play in fantasy baseball leagues who also have published numerous technical books, and I'll understand that you've got a real audience in mind."
Most of the sites which are popular so far are for nerds, because the nerds are coming from meta.stackoverflow.com. There isn't anyone else coming from anywhere else. I know there are lots of people who would post to a woodworking group, but the intersection between nerds and wordworkers is small. Thus the woodworking proposal has only got five followers so far. The whole business about saying "Oh you have to make a site for professional master woodworkers", which is supposed to win everyone over probably will make no difference. Also non-nerds don't know the stackoverflow system of questions and answers with votes, so they won't see the point: they will just see it as yet another boring forum.
You should absolutely not propose anything that a moderator doesn't like, or he's going to close your proposal even if it fulfilled all requirements and was well into the "commit" phase.
Now, of course it's not clear what moderators like or not like, so it can get tricky... but you can be quite sure they don't like fun :-/