Get a Distribution Deal or Sales Deal First
The film business is not much different to the building development business in that no one builds a 40 Storey building until they know that at least half the building has been let to long term tennants.
It’s the same with a film. A resonable standard feature film production will cost as much as medium size industrial/commerical building. Investors know how they will get their money back with a building, its called rent and if that fails, the building can be sold and the money recovered that way.
So don’t spend a cent on production (you have to invest in the script first) until you know that half the film is sold. i.e. you have distribution or sales deal, signed sealed and delivered.