Gilligan, 24, is an artist who works primarily in painting, drawing and collage. She studied at the Victorian College of the Arts, has exhibited regularly in solo and group shows, and her work has been acquired by the National Gallery of Australia. She is a regular contributor to Tavi Gevinson's online magazine Rookie.

Time After Time might be tied to the theme of fashion, but it turns out to be filled with many of the things that Gilligan loves. It begins with an evocation of the dress-up box that she remembers delving into at the age of four, an old army-green, canvas-and-leather chest which her mother and grandmother had filled with clothes and accessories she could explore.

The dress-up box is a motif for the contents of the book, for its blend of fashion, style, memory, identity, play. Dressing up, which began in childhood, continues to be a creative preoccupation. "It's about embodying a character you have made up or are referencing, and that's carried through into the way I dress, and a lot of other people do now. It's performative, and it's also a sentimental kind of vocation, perhaps."

Time After Time is vivid and nostalgic, personal and outward-looking, light-hearted and reflective, filled with pop culture references, family folklore, op shop counsel, offhand observations and wistful recollections. Gilligan has created pages of "mood boards" for inspiration. She is photographed wearing the outfits she has curated. she has illustrated backgrounds for the fashion spreads, as well as devising narratives around the outfits and describing the ideas and images they evoke. The outfits reference anything from fictional characters to songs, dream destinations to movies. There's one dedicated to op artist Bridget Riley (a rare instance of a black-and-white outfit), another that draws together, among other things, the Muppets, Linda Ronstadt, Bob Dylan, a blue dress, a gold purse and the song Blue Bayou.

Gilligan is a devotee of op shops, an avid collector of ephemera. There are eras that preoccupy her – the '60s and '70s, the world of polyester, psychedelia and brilliant colours – but she's also interested in contemporary designers, and she likes to combine them. Collage is an art practice, and a way of dressing too.

Gilligan has had a blog for several years, and found that its tone carried over into the text of her book. "I didn't know the form the writing would take until I started," she says. "But I wanted the outfits to have stories and references, and to explain where I was coming from. I thought the visuals would be the overarching thing, but the writing became more important as I went on." She wanted a tone of lightness and optimism that was "hopefully appropriate for younger readers and has something to offer older ones. "I wanted it to be open and playful, to encourage people to concoct their own outfits, feel it's legitimate". Part of her intention was "to get across the message that it's about how you want to feel, not about external forces dictating how you should look or feel."

Music is a strong element of the book's identity. Gilligan plays in a band, Pamela, with artists Jon Campbell and Georgina Glanville, and her work is suffused with personal musical associations and references. "I'm very sentimental, very romantic, I write about things like the seasons changing and I'm always associating this with songs, usually songs I experienced not when they came out, but later – through my parents or discovering them online."

She gives titles to her more abstract art work "that add context and references points, perhaps sometimes even a narrative", and she was keen to find the right one for the book. Her mother suggested Time After Time, and it seemed the perfect fit: it's the name of a Cyndi Lauper song from 1983 (with a reference to a "suitcase of memories") but it's also a phrase that suggests nostalgia, revisiting, the juxtaposition of eras and ages.

Gilligan has enjoyed the discipline of devising and producing the book, she says; it has also clarified for her the difference between her illustration and fine art work. She is happy to get back to working on a larger scale, painting again. "It's so different, and I really enjoy the freedom, the space, being unrestricted, without specific outcomes." She moved into a studio at Gertrude Contemporary late last year. Being there, she says, "is a symbol of being accepted as a fine artist, a rite of passage that I wanted to experience." She is working towards a show at Gertrude Contemporary Studio 12 in November, her first of the year.

Time After Time is published on September 1.