The right age for adoption
A kitten shouldn't leave its mother before 8 to 12 weeks: that's when it learns to use the litter box, to play and to pick up social cues. Adopting too early encourages behavioral problems (biting, fear). Go for a kitten that's weaned, vaccinated and already handled.
The essential supplies
A litter box (and its tray, away from the food), water and food bowls, a cat tree or scratching posts, a bed, toys and a carrier. Place the resources in quiet areas: a cat likes having stable points of reference.
Food and health
Choose food made specifically for kittens, rich in protein, and stick to the same brand as the breeder at first. Fresh water available at all times. On the health side: first vaccinations, deworming, parasite treatment and microchipping — then neutering around 5-6 months, strongly recommended for health reasons and to avoid unwanted litters.
Making the home safe
Windows and balconies: put up nets, a kitten has no sense of heights. Put away cleaning products, electrical cords and toxic plants (lilies, dieffenbachia…). Give it a 'refuge' room for the first few days before opening up the whole home.