We strongly prefer people to join existing projects rather than create new ones, but if you feel equally strongly about starting your own project, here are the requirements for applying for project hosting:
1) You must demonstrate significant progress on your project. Examples of significant progress would be a modeldump or demo release, or evidence of strong and detailed internal project organization.
2) You must have a campaign outline. (You don't have to release it publically, just show it to the person evaluating your hosting request.) It can be detailed or vague, but it has to lay out a plan of attack. This ensures that projects will make progress and will not wander aimlessly for years before settling down with a design.
3) If you want to be listed as a "hosted" project, then you will need a website, or a project page that people can visit to view story, screenshots, news, and so forth. It doesn't have to be very big, or very complex, but it has to be halfway decent, not something you threw together in five minutes. All hosted projects are given their own subdomain on hard-light.net.
4) We will not approve new project requests from any projects with campaigns longer than 20 missions. History has shown that the failure rate for such campaigns has been very, very high, probably upwards of ninety percent. Of those campaigns that do eventually release something, most languish for years, often going through one or more dormant stages before finishing.
5) Provision must have been made for what will happen if your mod does die. Too many campaigns have been hosted on HLP for several years only to end up unreleased. All the effort involved is then wasted, often because although there are many assets which could be released, people have moved on and can't be contacted and asked about making a public dump.
6) The team must have a clear policy over who owns assets while the mod is being worked on and after release. Releases that use Creative Commons or some other license which allows other members of the community to use the assets after release will be looked upon more favourably.
The object of this policy is not to discourage projects per se, but to ensure that the energy expended on projects is profitable and productive. There's nothing worse than pouring months and months of effort into a bloated albatross only to have it die off or be abandoned. Smaller campaigns of 5 to 10 missions have a much higher chance of succeeding.
It is also worth noting that FreeSpace has been out for a long time. If you have an idea for a fantastic new campaign of epic proportions, chances are pretty good that someone, or several someones, has already thought of it. In this situation, you're much better off finding an existing campaign similar to your own and joining that instead.