Spend a lot of money on advertising.
At least relative to the budget.
Raise, or save, at least 50% above the production budget to use for the exploitation and marketing of your movie.
This will radically increase your chances of success.
When times are tough, and money's short, that's the time to increase spending on marketing.
The reasoning is simple: people are not buying because they don't know about your product, or don't care about your brand at the moment.
Advertising makes them care.
Nike calls it "Demand Creation."
So if you're making a feature for $500... spend an extra $250 on marketing.
If you're making a feature for $1,000... spend an extra $500 on marketing.
If you're making a feature for $10,000... spend an extra $5,000 on marketing.