Every director wants final cut privilege. What this means is: they have control, the final say.
There is no certain way to make sure you have it unless you produce and fund your own work, otherwise, it's a struggle.
If you're a new and upcoming film director, the concern of producers will be that, due to your inexperience, they need to have the rights to the final edit in case you mess up or don't deliver a strong ending.
Paradoxically, the more financially successful you are as a director, the bigger the budget, the more responsibilities you carry. A studio won't want to spend a hundred million dollars and then let the director have complete freedom.
It's not uncommon to see extremely great debut feature films from writer/director's, who then go on to do uninspired big budget studio films. Often, this is because they have lost the freedom, the control. The decisions are made by producers, studio heads and focus group data.
Because who should control a film? Easy for us to say "the director!". But it's the producer who gets sued if the film doesn't get delivered. It's the investors who lose out if the film is unwatchable. Even when you give a great director the final cut, he won't always make 'Annie Hall'. Sometimes you'll get 'Cassandra's Dream'.
That's why the new crop of director's cut their teeth on low-budget short films. They learn the craft and build up a body of work to prove they know what they're doing. It's a producer's job to know what sells but it's a director's job to know what resonates. You just need to decide what kind of project yours is.
If you're directing a small independent film, you need to do everything you can to ensure you have the final cut privileges. It's your attempt at telling a story, it's your vision. No producer or investor could ever know how to nail your vision. You need to hold onto it at all costs and get it in the contract. That's why the festivals and awards and YouTube 'likes' are important, they prove your talent, your understanding, your ability.
You need to build a reputation as an artist. Never go over budget, and confidently stand by your vision, otherwise you'll get eaten. Then again, the truth is that the vast majority of films aren't art, they're product. If that's where you're going, then don't worry about final cut, you'll certainly have an easier time getting hired. But you may never get to make 'Annie Hall'.