Molly Weasley's badassery has been foreshadowed for a long time in Harry Potter — the first notable instance being her Howler to Ron in The Chamber of Secrets. Managing a household with so many children and doing the job perfectly, while being a member of the Order of the Phoenix, would seem an impossible task - but Molly is more than capable.
She's a classic Gryffindor, rushing into battle with as much vigor as she disciplines her kids with. Harry has admitted that Molly is the person he feels the most maternal warmth from, and it's not a surprise: she is an excellent mother to all of them. Although Molly usually offers useful and/or sensible advice, this isn't always the case.
Best Advice: “A Good First Impression Can Work Wonders.”
As Harry prepares to face the Wizengamot for his "illegal" use of underage magic, he begins to lose composure rather quickly, his thoughts devolving to fears of expulsion.
Molly tries to help him calm down, ironing his clothes and asking him to wash his hair, because "a good first impression can work wonders." She would be right in almost every scenario, except this case had been rigged against Harry from the very beginning.
Worst Advice: Warns The Twins Not To Blow Up A Toilet
Molly bids each of her children goodbye, embracing Percy warmly but when it's the twins' turn, she warns them to "behave themselves" and not to blow up toilets. Fred and George express their astonishment at her statement, claiming that they had never performed such a prank.
Unfortunately for Molly, she may or may not have planted the idea in her children's head, and knowing those two, a messy outcome is guaranteed.
Best Advice: When She Helps Harry Go Through Platform 9 3/4
Eleven-year-old Harry, freshly introduced to the magical world and all its complexities, finds himself stranded at Platform 9 3/4, until he spots a group of red-haired children disappearing into a barrier.
Harry goes up to the mother, obviously Molly, and before he can even finish explaining his situation, she tells him how the transport works. Molly reassures him in her calm voice, asking him to "run if [he's] nervous", and that it's important not to stop or "be scared."
Worst Advice: Instructing Harry On Floo Travel
The problem in this situation is not Molly's lack of clear instruction, although she doesn't prevent it from being muddled by advice given by Ron, Fred, and George simultaneously. She tells him that he "must speak clearly... and get out at the right grate," without telling him what a grate is or how to identify one.
Arthur asks his wife not to "fuss", but Molly continues with a barrage of points ranging from keeping his "eyes shut" and not to "panic and get out too early; wait until you see Fred and George.” Harry barely manages to enunciate the words "Diagon Alley", thankfully, because a misstep could have led to disaster much worse than just ending up in the wrong spot.
Best Advice: Forbids Her Children From Questioning Harry On Inappropriate Subjects
Fred and George are gleeful to learn that the famous Harry Potter is finally at Hogwarts, and they confirm this fact to their mother by mentioning "his scar... like lightning."
Molly's first instinct is to fret about him, expressing her sadness that "he was alone." The twins dismiss her, asking if he would "remember what You-Know-Who looks like." Their mother furiously tells them that they had better not bring the topic up in conversation with Harry, let alone "on his first day at school."
Worst Advice: Preventing The Order From Revealing Information To Harry
Molly tries her hardest to prevent the younger members of the Order from learning about the latest Voldermort-based developments. She inevitably gets into an altercation with Sirius as to whether Harry should be involved. Molly is ultimately overruled by Dumbledore (via Lupin), so she shifts the ban on her children and Hermione.
Sadly, this doesn't work either, because Fred & George are "of age" at the time, and Harry declares that he will tell Ron and Hermione everything. Only poor Ginny is forced to face the brunt of her mother's understandable, but unnecessary, discipline.
Best Advice: Tells The Girls To Get "Out Of My Way!"
As Bellatrix begins to overpower Luna, Ginny, and Hermione, one of her Avada Kedavras passes Ginny "by an inch." Molly notices this from wherever she is, and screeches at the Death Eater while thundering towards her.
Bellatrix is all the more pleased to find a superior opponent, but her enthusiasm disappears as Molly orders the children to "get out of [her] way." The fight doesn't take very long, and thankfully, the three girls aren't caught in the thick of it.
Worst Advice: Tells Fred, George, And Ron To Be More Like Percy
Ron, Fred, & George take their dad's flying Ford Anglia to Privet Drive, where they intend to smuggle Harry out to the Burrow. They manage to escape by the skin of their teeth, but Uncle Vernon's impotent fury is no match for the overwhelming rage brewing in a worried Molly Weasley.
Her anger is incredible, making her three boys tremble before her wrath. Of course, Molly then goes on to tell them that they "could do with taking a leaf out of Percy's book." In her defense, she doesn't exactly know how Percy is going to turn out, but the signs have always been there.
Best Advice: When She Doesn't Even Use Words To Comfort Harry
Harry's experience at the conclusion of the Triwizard Tournament is arguably the worst he has endured in his entire life. Not only does Cedric die, but Lord Voldemort makes a triumphant return using nothing other than Harry's own blood.
Wracked with guilt, the Boy Who Lived Again is about to burst into tears when Molly tenderly whispers that "it wasn't [his fault]" and proceeds to "put her hands around Harry". The narrator then explains that "he had no memory of ever being hugged like this, as though by a mother." Sometimes the best advice, like the best spells, is non-verbal.
Worst Advice: About Youngsters "Whipping Their Wands Out For Everything"
When Fred and George are finally allowed to use magic outside Hogwarts, they start casting spells and disapparating for the simplest things. Molly does not like this at all, and she refuses to consider that almost all youngsters (or people in general) would behave in this manner when suddenly handed access to new power.
When the twins enchant a set of utensils and cutlery to fly from the kitchen and into the dining hall, Molly yells "JUST CARRY THEM!", which is when everything comes crashing down. Is it because they were distracted by their mother? Nobody knows.