The Light Fantastic is the second book in the Discworld canon. Similarly to the colour of magic it follows Rincewind and Twoflower on their adventures around the Disc. It really should be called "more of the colour of magic" but that's not so snappy is it?
It still operates slightly outside of the Discworld we know these days, though several ideas an characters are introduced that will turn up again and again - death becomes more like the Death of later, with his daughter Ysabell who will crop up again several times over, and Cohen the Barbarian who is possibly the best take on the traditional Barbarian fantasy shtick in existence makes an appearance.
Not a wonderful fit by Discworld standards, but certainly a strong foundation for the canon and an enjoyable fantasy novel that recognises the clichés of the genre and uses them out of spite.
Equal Rites, the third book in the series and the first of the 'witch' stories, is to my way of thinking also the first true Discworld novel, in the way that I view them. It is a satirical and considered look at genuine social issues through the lens of fantasy and humour, in this instance on the subject of "boys clubs" and rights for women, as well as formal and informal education and the place of academia in real world subjects.
The eighth son of an eighth son is inherently a natural wizard. This is important, so remember it for later books. What has never happened before is that this eighth, eighth son is actually a daughter, and without a right of entry to the men-only world of the wizarding school of the Unseen University there's no one to teach Esk how to control the magic within herself.
That means the job is left to the witch Granny Weatherwax, until she can't manage the forces alone and is forced to take Esk to the University, whether the wizards like it or not. The story deals with the little things, like monsters from the darkest edges of reality and the end of the world, as well as the big things such as why witches are intuitively magical and can commune with the world and why wizards are obsessed with quantifying the magic around them, and why both are more magical when they aren't actually doing any "real magic".
This is book 3 out of almost 40 novels, so there's still a lot of changes I know from reading later stories to expect, but it is a true, fully canon, story to my mind. Funny, dark, and heavily laced with the kind of savagely accurate satire that you can read without realising how much it is undermining the world around us. I'm enjoying my trip through the Discworld, so far.