LOS ANGELES (Hollywood Reporter) - Elizabeth Banks had a request for her producers when she shot her first scene as a guest star on NBC's "30 Rock."
Banks was playing CNBC anchor Avery Jessup, and the scene involved her meeting executive Jack Donaghy (Alec Baldwin), making a rapid-fire appearance on her "Crossfire"-like news program. The actress knew her lines, but wanted to deliver them as quickly as she could.
"I begged them to put it on a prompter for me," she says, noting her quick delivery would help sell the comedy and her character. "They said, 'No problem.' But I got there that night and there was a problem. They couldn't figure the prompter out! It came down to me throwing fastballs at Alec and him battling them back as fast as possible and hoping they could cut it together faster than we were doing it."
Tough, but Banks pulled it off -- and doing so gave her an epiphany. "It was my 'I belong here' moment," she says. "There are shows where you show up and they want you to service the (other) actors, and that's not '30 Rock': They want the guest star to be funny. That's why they get great guest stars."
Being a guest star on a show that has been humming along for several seasons often comes with benefits: The writers know the voice of the show, series regulars are comfortable with their characters, and everyone on set has dealt with guest stars long before you show up. But there are some challenges for guest actors as well: Will they fit in, will they get the cadence, or worst of all, will they mess up a good thing?
Jared Harris, who guest-starred as British invader Lane Pryce on AMC's "Mad Men," says he was attracted to the period drama's strong writing, which he calls "sort of a blessing and a restriction." A show known for its specific scripts and creator Matthew Weiner's exacting attention to detail, "Mad Men" was a place where Harris felt he would need to deliver.
"They knew the world so well, which is great but a little intimidating," he admits. "Everyone has a shorthand and you're trying to get up to speed. You're only given the one episode to read. They're all extremely friendly and nice and welcoming, but trying to figure out who the character was, that took a couple of episodes just because there wasn't a lot of material yet."
The 1960s elements worked in Harris' favor because it reminded him of the world he grew up in, and of his stepfather, who became a model for Lane. "I never realized I would feel grateful to my mother for marrying Rex Harrison," Harris quips of the "My Fair Lady" star.
With his stepfather as his guide, Harris quickly figured out Lane, which he thinks inspired Weiner to invest so much in him. (Lane is a series regular for the upcoming season.) "If Matt likes what you do and he responds to your character and you excite his imagination, he'll start writing for you more," Harris says.
Of course, knowing that creates added pressure: "You got the job, but you're still auditioning."
Shows like "Mad Men" and "30 Rock" are newbies compared to "Law & Order: SVU," where five-time Emmy nominee Ann-Margret guest starred during the show's 11th season as Rita Wills, a faded model stuck in the past.
A self-described fan -- "I even watch reruns during the day, I'm so avid," she says -- the actress was struck by how steady the production was. "I was really looking forward to seeing how (co-stars) Mariska (Hargitay) and Chris (Meloni) were getting along," she says. "I was so hoping they were still great friends after 11 years, and it's true."
That longevity extended beyond the cast. "A lot of the crew has been there since inception," she says. "Some of the crew has been there nine, 10 years, and that tells you what it's like."
This kind of stability creates an environment where a guest star feels comfortable, she says -- something crucial given how quickly guest stars are plunged into deep emotional moments. "They knew how difficult this character was," she adds. "I have never played a woman who was an addict, an alcoholic and a hoarder."
Besides support, the atmosphere on set allowed the actress to experiment with her character. During one of the show's classic interrogation scenes, she suggested her character produce a flask, a move director Helen Shaver quickly embraced. "They were with me every step of the way," Ann-Margret says. "They readily accepted it."
Kristin Chenoweth has been through the guest star gauntlet numerous times, but most recently on Fox's musical breakout "Glee." The actress filmed her first episode before the show premiered, then reprised her role as the boozy April Rhodes after "Glee" became a hit.
"You work a lot, but the good news is I love to work," she says of the show, where delivering multiple song and dance numbers is a typical day's work.
For Chenoweth, one of the challenges of being a guest star is remembering the week on set is a marathon, not a sprint. "Definitely come in with energy, but you're going to be doing a lot of waiting," she warns. "You come out of the gate like a thoroughbred, but you have to be very careful not to give it all up in the beginning. When you have a break, take it. If you're always up and always ready to go, you shut down and you wear out real quick."
Playing opposite an established, well-loved character can also help a guest star get up to speed.
Gary Cole benefited from that on HBO's "Entourage," where many of his scenes had him playing his character, the somewhat hapless agent Andrew Klein, off Jeremy Piven's type-A Ari Gold. "face-to-face with an iconic character," Cole says, "you're automatically legitimate. I became the beneficiary of that."
But Cole rejects the idea that being a guest star requires an actor to take a different approach than on some other job. "To me that doesn't really define anything," he says. "Your function is to come in and make whatever scene you're in work and be believable."
For Cole, that's just another day of work. "I've been around enough and walked into enough new situations that there is nothing really to that," he adds. "Any job you walk into is new."
Still, Banks says there's an etiquette that she finds useful when guest starring, a gig she pulled this season not only on "30 Rock" but also ABC's "Modern Family."
"The title 'guest star' says everything," she says. "You're a guest in someone else's house and you have to act that way. I treat it as (if) I'm visiting someone's house for the weekend -- make the bed before you leave, be nice to everybody and know your place."