Have more than just a concept on paper for your film. You should have a completed screenplay and know every plot point so that when you begin pitching the film to a possible investor, you do not stumble over any questions he may ask about your film.
Film a trailer of your movie. Put together a cast and crew and create a short version of your film. This doesn't have to be more than five minutes long, but a trailer is a selling device. Trailers show that not only do you have a talent for movie making, but also that the film you want to make will be interesting and have box office appeal.
Start looking for investors among your own family and friends. Often, they can help you come up with the funds that you need, even if it is a small amount from each individual---especially if you offer them a co-producers credit on the film, which many people will think is a real thrill.
Network at local film festivals. Have your pitch ready. Offer to send DVD copies of your trailer. Chances are someone in your town or state is a strong independent film supporter. Pitch your film idea and possibly secure the funding you need from a single source. This type of investor is known as a "super angel" because they are able to invest as much money as needed to get the film made.
Negotiate a negative pickup deal with a production house. While you will have to finance the film yourself until the production house pays for the rights, bank loans are easy to secure since there is a contracted deal in place. Once the deal is completed, the loan can be repaid in a single lump sum. Having a completed script or trailer is essential when pitching your film to a production house.
Approach banks and insurance companies that are already involved in the film industry. Often these outlets are overlooked, but if you have a film that is possibly a blockbuster hit, many banks and insurance films will look at your film as a possible investment.