Welcome Episode

The standard Premiere plot, which makes up about 75% of TV premieres and pilots, in which a single new member comes into an established group. This gives the writers an easy way to introduce the characters and all the most relevant facts about them as the new member, as ignorant as we are, gathers information. If the group is a workplace, more often than not the new member is a Naive Newcomer.

Examples of Welcome Episode include:

Anime and Manga

Ranma and Genma Saotome move into the Tendo household in Ranma ½.
Yukito in AIR comes into town and meets everyone in the first episode.
Sasahara and Kosaka in Genshiken.
Linna in Bubblegum Crisis: Tokyo 2040.
Naive Newcomer Ai Tanabe in the Planetes anime. The manga starts several months before her arrival.
Contrast the above with Noa Izumi of Patlabor. Heck, Planetes is Patlabor IN SPACE!!.
Guts in the second episode of Berserk, as the entire anime series is set up as a How We Got Here for the very first episode where Guts is the Black Swordsman, a Demon Slaying, BFS-wielding Badass out for revenge against his former best friend.
Ebisu from Ebisu-san and Hotei-san is introduced this way when Ebisu transfers from a corporate city head office to a local suburban branch office.
In the very first episode of the Kirby anime, Kirby crash-lands in Dreamland and is introduced to Cappy Town by Tiff, Tuff, Lololo and Lalala and welcomed to it by the Cappies. They even build him a new house for him to live in in the second episode.
Hanaukyo Maid Tai. The first episode of each series, as Taro becomes the new head of the Hanaukyo family and meets the mansion's maids.
So Ra No Wo To‍'‍s first episode is about the main character meeting pretty much everyone and walking around the setting.
Miho Nishizumi transfers to Oarai Girls High School in the first episode of Girls und Panzer, and the Absurdly Powerful Student Council forces her into a particular school club.

Comic Books

Clark Kent in Legion of Super-Heroes.
Toybox in the first issue of Top Ten. Later played very differently when Joe Pi joins the team.

Fan Works

Calvin and Hobbes in Calvin at Camp.

Film

J in Men in Black.
Another: Myers in Hellboy.
Duke and Ripcord in the G.I. Joe Live Action Adaptation.

Literature

Maze Runner starts with the protagonist having amnesia and being unkindly welcome by the surviving group in the maze.

Live-Action TV

Mr Parker in McHales Navy
Kyle in Kyle XY.
Sally in Sesame Street.
PC Carver in The Bill.
Carter in ER.
- Also the reboot of sorts with Lucy Knight at the start of season 5.
Rachel in Friends (although she already knew Monica and Ross -- and was subsequently revealed to have already met Chandler a few times as well.)
Elaine in Taxi.
Diane in Cheers.
Tim Bayliss in Homicide: Life on the Street.
Buffy in Buffy the Vampire Slayer.
Jenny in The L Word.
Ryan in The Office (US).
- Ricky in The Office (UK).
Dave in News Radio.
Lacey in Corner Gas.
Dr. Fleischman in Northern Exposure.
Carter in Spin City.
Maya in Just Shoot Me.
Mary in The Mary Tyler Moore Show.
Jeremy in Sports Night.
CSI subverted this trope in a major way by having a Welcome Episode premiere which ended with Naive Newcomer Holly Gribbs getting shot dead.
- Then played straight when Sara Sidle is brought in to replace her/act as an independant investigator.
- Then played straight again when Ray Langston joined the team.
CSI: NY did it with Lindsay. She kept getting all the messy jobs, even after the first ep,and eventually remarked to Mac that it was getting a little old.
Jack Carter in Eureka.
Ty Davis and Carlos Nieto join the NYPD and FDNY respectively in the first episode of Third Watch.
Beecher in Oz
Ian and Barbara in Doctor Who. Rose in the 2005 relaunch.
Gwen in Torchwood.
Simon, Book and River in Firefly
Dr. Caroline Todd in Green Wing.
Elaine Nardo and John Burns in Taxi. Oddly enough, John only sticks around for one season.
Vorlon Ambassador Kosh in Babylon 5 (Technically Lyta Alexander as well, but her character disappears for two seasons)
Steve and Marcy Rhoades in Married... with Children.
KC in Vengeance Unlimited.
Agent Cooper in Twin Peaks.
Betty Suarez in Ugly Betty.
Andy Travis in WKRP in Cincinnati.
Dick and Joanna in Newhart.
The first episode of Thirty Rock featured both Jack Donaghy and Tracy Jordan meeting everyone else. This is a bit of an untraditional example in that Jack and Tracy are about the most insane characters on the show and everything was (relatively) pleasant before they came along.
The eponymous Merlin.
Annie, and, in a sense, the flat, in Being Human (UK).
Power Rangers uses this tactic with their Rookie Red Rangers in seasons 10 (Wild Force) and 13 (S.P.D., with slight modifications to the formula).
Chuck in Pushing Daisies.
Done in How I Met Your Mother, with whom is somewhat up to debate, with Robin joining the existing group, but the kids being the ones who are getting the information about everyone.
Will in the Britcom The Inbetweeners.
Amy in The A-Team
The eponymous writer in Castle
Elle in Criminal Minds. Ironically, she only lasted one season, and the show continued without her.
Dr. Will Zimmerman in Sanctuary.
Josie in Strange Days At Blake Holsey High/Black Hole High.
Frank in Are You Afraid of the Dark?.
Penny in The Big Bang Theory.
Jess in New Girl.
Number Six, the eponymous prisoner in The Prisoner, joins the other prisoners in The Village in the pilot episode.

Theatre

In both the movie and the original Broadway production of 1776, Dr. Lyman Hall of Georgia is only a supporting character, but his arrival in Philadelphia provides an excuse for the rest of the cast to introduce themselves to him (and to the audience).

Web Comics

Chapter One of Everyday Heroes, where Mr. Mighty and family meet the neighbors. Also in Chapter Three, where he finally gets around to meeting the rest of his teammates.
In the Whateley Universe, the intro stories for Sara Waite (Carmilla), and then Chou Lee (Bladedancer), as they meet the rest of Team Kimba.
Willow, new arrival to Earthsong.

Western Animation

Theodore Tugboat.
Sam Dullard in Rocket Power.
Doug Funnie in Doug.
With the exception of a Poorly-Disguised Pilot episode of Spider-Man and His Amazing Friends, the various animated incarnations of X-Men invariably use this technique:
- Kitty Pryde in the abortive animated pilot "Pryde Of The X-Men".
- Jubilee in the 1990 series.
- Kurt "Nightcrawler" Wagner in X-Men: Evolution.
  - A new character was introduced in each of the first five episodes, making this a Debut Queue.
- Wolverine and Rogue in the first movie...
- ...and even Jean "Marvel Girl" Grey in the first issue of the original comic. The introduction of the "All-New, All-Different" team in the '70s, however, was Everyone Meets Everyone.
Fry in Futurama (2 episodes worth of welcome! The first introduces him to the trio of other central characters while the second introduces the rest-Amy, Hermes, and Zoidberg)
Firestorm in The Legendary Super Powers Team
Cyborg in Galactic Guardians
Green Arrow on Justice League Unlimited.
Kevin in Mission Hill
Mac and Bloo in Foster's Home for Imaginary Friends.
Caitlin in 6teen.
Hal Jordan especially in the animated adaptation, introduces the audience to the Green Lantern Corps this way.
Dudley Puppy in Tuff Puppy.
The Powerpuff Girls pilot "Meat Fuzzy Lumkins" has narrator Ernie Anderson entreating us to say hello to Blossom, Bubbles and Buttercup.
Gus Griswald in the Recess episode, "The New Kid". What's different is that it's episode 1B (following a Two Shorts format) instead of episode 1A.
Twilight Sparkle in My Little Pony Friendship Is Magic. This gets coupled with Twilight and her newly formed friends gathering the elements and defeating an Eldritch Abomination.