Finalize your script and make a comprehensive project proposal. Have a handy one-page abstract that serves as your guide when pitching to potential producers and grant-giving agencies. It is never easy to convince others to shell out money for a project. You must impress them with your presentation and proposal. If you can, make a spec trailer that they can view on DVD or online. A film reel or sample work are also very helpful to gain credibility. These will allow funders to gauge your filmmaking skills and will also offer an initial glimpse of your film's potential. Your project proposal should include a production budget breakdown and preferably a storyboard as well. Have an initial list of your production team (cast and crew) and provide brief professional backgrounds for each person.
Apply for film grants. Get information about calls for grant submissions through websites, film groups and magazines, TV and print advertisements and through word-of-mouth within the independent-film circle.
Seek sponsorships, solicitations and x-deals (exchange deals) from companies, arts supporters, philanthropists or even friends and relatives. Furnish all the supporting documents and present your concept to them and tell how they can benefit from such sponsorships and x-deals. Solicitations don't necessarily require something in return, but it's always good to note in solicitation letters that the funder will be included in the film credits. If you're a film student, you have some advantage because you can get endorsements and recommendations from your professors, and there's a chance you can use your school's letterhead to make your documents look more professional and official. Also, go back to your story and look for possibilities for product placements, then pass on proposals to potential sponsors and advertisers.
Try getting appointments to pitch to movie executives and producers. It is very tough to get appointments with these people, but it's always worth a try. Try pitching to independent film producers, who are more open to short film projects.