After scoring a sleeper success with 2012’s “Sleepwalk With Me,” which adapted his solo stage show about toiling on the standup circuit, writer-director Mike Birbiglia stretches out a bit — but not too much — with the accomplished seriocomedy “Don’t Think Twice.” Like its predecessor a pleasingly naturalistic insider’s view of life on the lower rungs of showbiz, this more ensemble-focused piece is also somewhat autobiographical, as it draws on Birbiglia’s background training and performing with improv groups. But here a fictive scenario develops in which one member of a longtime improv troupe suddenly wins the comedy lottery of a cast gig on a “Saturday Night Live”-type sketch show, throwing those colleagues left behind into turmoil. This realistic but not excessively downbeat portrait of fame striking a lucky few — and missing everyone else — should build on “Sleepwalk’s” fandom to decent niche returns in various formats. Friendship revisited. The cast including Kate Micucci, Chris Gethard, Gilian Jacobs and Keegan Michael Kay.