Bradbury discovered SF fandom in his youth, meeting Ray Harryhausen, Forrest J. Ackerman, and Henry Kuttner, and began publishing his fanzine, Futuria Fantasia in 1939. His first professional sale was the story, Pendulum, with Henry Hass for Super Science Stories. In that year he met Leigh Brackett, who generously coached him in writing techniques. He later collaborated with her, completing her Lorelei of the Red Mist. Ms. Brackett wrote the first half, and Bradbury completing it. It's sort of a space opera romance. I haven't read it, but here's a synopsis:
Hugh Starke, space-rat and convict, was being pursued by spacecraft into the unknown parts of Venus. He had just pulled off the largest lone wolf heist in the history of that planet. But now it looked like he was going to pay the ultimate price for his misdeeds. But fate had a strange twist on Starke's life when he woke up in a different body. A body that was strong and powerful. In a body of a Venusian barbarian named Conan. But was Starke anything more than a puppet in this new body? For he soon found out the strings were being pulled by the beautiful, but terrible, Rann. For Rann was like the siren, Lorelei, and it was Hugh-Starke-called-Conan that would have to fight her or be lured to his doom.
By the 40's Bradbury's style started to jell blending poetic and evocative elements, consciously symbolic, with strong nostalgic elements and leaning towards the macabre, some would say his writing is less SF and leans more towards fantasy and horror or weird fiction. One story, The Million Year Picnic, appears in The Martian Chronicles, which is one of his more famous books. It has interwoven stories, which tell of humans trying to colonize Mars. It was later made into a TV miniseries.
Most of his work adapted to film is fairly worthwhile. Two early B-movies were loosely based on short stories by him: It Came From Outer Space and The Beast From 20,000 Fanthoms. Two other films from his books were The Illustrated Man, which is about a man covered in magical tattoos, that spring to life. The other is Fahrenheit 451, a film directed by Francois Truffaut, is a dystopian future where books are burned that are deemed dangerous. One of the main characters is a fireman that does some of the book burning, until he has an epiphany and sees the error of his ways. From what I've read Bradbury was not happy with the way Fahrenheit 451 was adapted to screen, but I've always enjoyed the film.