Write a good script. Keep costs low by focusing on characters, situations and witty dialogue, not effects, lots of settings and stunts. Look for a world to show us that the movies don’t often visit.

With a little luck, good actors will come to you and your indie film is as good as made.

“Thelma” is an indie comedy that proves a lot of the truisms of “How to make your debut feature film.” The most adorable “action” pic of the summer is a senior citizen’s caper comedy that’s novel enough and clever enough that the fact that it also has something to say is merely the cherry on top of the cinematic sundae.

The further it putters along, maintaining forward-motion at senior citizen speed, the cuter and more surprising it becomes, and the more we understand why Oscar nominee June Squibb and five other “names” signed on, why the money to make it came together and why its headed to a theater near you.

We’re all going to get old. We’re all going to be victimized, probably online. And we all want our revenge.

Squibb has the title role, an LA 90something who has been widowed a couple of years and is still keeping her apartment. She’s active and mobile enough, even if she can’t drive. But her world has shrunk. Her peers have mostly passed on.

She has that habit of the extremely elderly, blurting “I think I KNOW her!” about most every person of advanced years she sees. That always starts a conversation, almost always with someone it turns out she doesn’t know.

“If I fall, I’m lost,” she knows, passing on that mantra of everyone’s dotage. “It’s why I don’t fall.”

She seems savvy enough with her iPhone, but needs doting grandson Danny (Fred Hechinger of “News of the World”) to help her get her laptop going and email operating. That’s probably how she’s exposed to the scam.

“Danny” calls, in a rush. Says he’s been in an accident, he’s in jail and a lawyer’s about to call. The “lawyer” calls, demands $10,000, gives her an address and the bum’s rush and hangs up.

And with Danny, his mom (Parker Posey) and Dad (Clark Gregg) not answering their phones — only seniors answer calls from strangers these days — next thing we know, she’s raided her cash-stashes around the house, stuffed it into an envelope, addressed it and waddled down to the post office.

Oh well. At least she’s OK, they tell her. “Nothing you can do at this point,” they say to her face.

“These things happen to people her age,” they say behind her back, but within earshot.

With the police yawning about her crime, her family just relieved she’s safe and no peers she can call for help, Thelma takes inspiration from the action star of a movie her grandson just watched with her. Like Tom Cruise, she’ll do her “own stunts.”

First-time feature writer-director Josh Margolin sets up problems, builds comical (and serious) suspense in, and foreshadows solutions. No car? That widower whose calls she doesn’t return mentions his new “scooter.” Ben is in a nursing home, lonely, and realistic.

“We’re old. Diminished. A liability to the ones we love.”

It’s not like Thelma’s enlisting his help. Getting Ben’s scooter is merely another obstacle on her quest.
But Ben is played by the late Richard Roundtree, in a fitting and fun final performance. That’s an accomplice well worth enlisting.

“Thelma” has our heroine visit an old friend who’s become a shut-in, and stumble into more than one “I think I KNOW her!” The indignities of great age, outliving your peers, coping with an ever-changing world via a shorter and shorter attention span and helplessness in climate where preying on the elderly is tolerated are commented on with resignation and wit.

“How can Zuck-uh-Berg let this happen?”

The narrative grinds almost to a halt in the middle acts, and there are head-scratching lapses in logic that hang over many a twist.

But Posey’s presence turns the family-squabbles about “Mom/Gran dma’s MISSING!” into ’80s indie kvetch-offs and the running gags pile on and everything — EVERYthing — we see coming we see coming for an amusingly excruitiatng long time.

Roundtree introduces pathos and gravitas to the proceedings. And a little muscle. Hechinger sparkles as a hapless, directionless and indulged 24-year-old racked by guilt, but the guy who gives granny the most credit for being able to get what she wants.

And Squibb holds it all together as a nurturing (smothering) mom turned doting granny, but transformed into a stubborn old cuss, simply by being preyed upon the way many of her peers are.

Her revenge is their revenge and their revenge is played out, at walker-scooter speed, to our delight in this winning, against-the-grain codger caper comedy.

Rating: PG-13, gunplay, profanity

Cast: June Squibb, Richard Roundtree, Fred Hechinger, Parker Posey, Clark Gregg and Malcolm McDowell.

Credits: Scripted and directed by Josh Margolin. A Magnolia Pictures release.

Running time: 1:38