Clint and Mel can do it. It seems Ben can do it. But Sly and Barbra can't. If you're a movie star who thinks it might be fun to direct a film, read this advice from Joe Griffinbefore you even look at a megaphone

IT'S fascinating to watch an actor take control of their career. That movie star is not just a talking prop, but a living, breathing thing with ambitions beyond acting. Sometimes, when given the opportunity to make their own films, they betray a deep conscience (such as Sean Penn), a sharp mind (George Clooney) or a rich imagination (Danny DeVito).

Other times, they betray a staggering lack of vision (Sylvester Stallone's direction is even more conventional than his writing), shocking narcissism, or an ignorance of audience demands (witness Kevin Costner's sci-fi epic about a postman).

Of course, acting and directing are two very different skills, and one would have to be psychic to spot a good director in a good actor.

Consider this contrast: Johnny Depp's choices in films often reflect a pure love of cinema, and sometimes artistic courage and integrity. But his little-seen directorial debut, The Brave(1997), left critics cold and struggled to get even a DVD release.

Ben Affleck, on the other hand, spent a decade acting in almost exclusively bad mainstream films, but his first directorial effort is the critically acclaimed, Oscar-nominated Gone Baby Gone.

For every success story, there are many more whose efforts led to public indifference. Nicolas Cage's only film as director, Sonny(2002), elicited barely a shrug from the public and the press.

Even actor/directors who emerge with a strong debut often fail to recapture the magic throughout their career: Denis Hopper's Easy Rider(1969) and Jodie Foster's Little Man Tate(1991) linger far longer in the memory than their follow-up films ( The Last Movieand Home for the Holidays, respectively).

Below are some of the dos and don'ts for actors-turned-directors. If you're a movie star who's thinking of picking up the megaphone, please read carefully.

DO

Toy with your image
Clint Eastwood in Unforgivenwas an ageing, broken cowboy in a film about violence, Warren Beatty in Bulworthbrought his famously liberal image to a wild hip-hop extreme, and Mel Gibson attacked his heart-throb status with unsightly scars in The Man Without a Face.

Use your star power
Some actors use their pull to pursue personal projects, many of which would not have been made without their involvement: Gibson's The Passion of the Christwas a big gamble with a big payday. Good Night, and Good Luck, a period piece in black and white about McCarthyism, probably wouldn't have been made without George Clooney's involvement.

Work to your strengths
Decide which you're best at: acting or directing. Long ago, mediocre actor Ron Howard decided to concentrate on his not-so-mediocre directing skills. Also, Gone Baby Gonesuggests that directing, not acting, is Ben Affleck's true calling. Compare Sofia Coppola's most famous acting gig ( The Godfather Part III) to her most famous directing one ( Lost in Translation).

Learn from your betters
Robert De Niro's A Bronx Talewas clearly influenced by his long-time collaborator Martin Scorsese, and was all the better for it. Clooney's films don't suffer at all for their meticulous Soderbergh-ian detail. Mel Gibson spent just about two decades starring in action movies; the mighty Apocalyptoshows that he was paying attention on set.

Cast yourself
Tom Hanks's playful supporting role in That Thing You Do!made the film both easier to finance and easier to enjoy. A young Orson Welles gave himself a star-making role in his directorial debut, Citizen Kane.

DON'T

Overvalue the acting
When the actor-director values acting over cinematography, editing and pacing, films, such as some by Ed Burns, Robert Redford and Woody Allen, end up feeling like filmed plays.

Be narcissistic
Woody - Mira Sorvino wouldn't kiss you in real life, nor in a film directed by anyone else ( Mighty Aphrodite). Barbra Streisand - having Pierce Brosnan drooling over you while Mimi Rogers gets jealous (in The Mirror Has Two Faces) only highlights how far removed you are from those beautiful people. Kenneth Branagh - 36 is simply too old to play Hamlet.

Try too much, too soon
John Favreau's films have become progressively more adventurous, from the low-budget buddy movie Madeto the blockbuster Iron Man. By contrast, Kevin Spacey's expensive Bobby Darin biopic, Beyond the Sea, was only his second film. Dan Aykroyd's even more expensive and audacious Nothing But Troublewas his first and last time holding the megaphone. The Alamo, John Wayne's first proper film as director, was a costly mistake for the Duke, who poured much of his own money into the project.

Overstay your welcome
Charles Laughton made only one film - The Night of the Hunter- but it's an unequivocal classic. Kevin Costner made three, one of which was The Postman. Even the respected Richard Attenborough hasn't directed a well-received film since Shadowlands.

Do it for the sake of it
You want to direct a movie starring you that's indistinguishable to your last film? Why? Stephen Seagal's On Deadly Ground, we're looking at you.