Hey buddy, are you on a movie set and have just looked around and realised that you're the only one who's realised that this film isn't going to make it? Well then, we have some advice for you.
First of all, I'd like to congratulate you on realising something that so few people do. Delusion is not good for the soul and it's never good to be surprised when the reviews come off. Second of all, don't think of this as a stumbling block in your career. Think of it as an opportunity to stand out. To steal this film out from under their rugs. Here are some observations to help.
The biggest warning sign is that this is an adaptation that shouldn't exist.
Adaptations of board games, video games, theme park ride, comic books, movies, for whatever reason (it's laziness) are often fighting an uphill battle to not be horrible. If you've found yourself on one that has failed that battle, get ready. You'll know if you're in Dungeons and Dragons instead of Lord of the Rings.
Or Dennis Hopper in Super Mario Brothers. Video game movies are going to show up frequently.
Play the villain.
This is your best hope of saving the film. Many a film has entered "so bad it's hilarious" territory because the person playing the villain decided to destroy the scenery. Let Alan Rickman in Prince of Thieves be your guide in this. Deliver every stupid line you are given with every bit of intensity you can find. This is how the line "Because it's dull, you twit, it will hurt more!" becomes a classic.
Have entirely too much energy.
If everyone else appears to sleepwalking through a nightmare of a film, you can save it by bounding about the set like a madman. Large hand gestures, sweeping capes, bouncing up and down — do it all and you will have all eyes on you.
Dress for success.
If you want to be the only memorable thing about a movie, wear something that someone who wants to be just obscure enough can turn into a vaguely recognisable Halloween costume. And if you want to make sure all eyes are on you in every frame, have a prop to draw the eye. Staffs are popular.
Lex Luthor made do with a crystal.l
Do you know what the best part of the Twilight films are? It's any scene with Michael Sheen. Any scene. Sheen's performance as Aro plays very much like he had a bet with a friend that he could render every shot he was in useless and the director never noticed. He's not just eating the scenery. He's not just running around manically. He is zigging where everyone else is zagging. The best three seconds of the entire series is him reaching for a child while laughing with all the dignity of a concussed Woody the Woodpecker. Here it is on loop for five hours:
Why did Sir Ben Kingsley do Uwe Boll's nightmare of a film Bloodrayne? Well, he said, "To be honest, I have always wanted to play a vampire, with the teeth and the long black cape. Let's say that my motives were somewhat immature for doing it." That's fine! If that's the reason you said yes, embrace the role, reject the movie.
I'm sorry about this one. There are a few non-British actors who have managed to bake and deliver ham with the best of them: Raúl Juliá in Street Fighter, Frank Langella in Masters of the Universe, Joseph Gordon-Levitt in G.I. Joe, etc. But the Brits own this category. Alan Rickman, Jeremy Irons, Christopher Lee, Ian McDiarmid in the Star Wars prequels, Kenneth Branagh in Wild Wild West, Sean Connery in The Avengers, Ralph Fiennes... the list goes on and on. If you're British, you're halfway home.
If you're in a teddy bear suit, talking to a table of people in teddy bear suits, it's time to chew the scenery. In all honesty, you've been given a gift. Yeah, there are films that are going to be well-reviewed and win awards. But if you want to give the most appreciated performance, it's being entertaining enough to save a film that would otherwise be a nightmare to watch.