A 4.0 mm (G-6) or 5.0 mm (H-8) hook works well for beginners.
Scissors and a tapestry needle (yarn needle) for weaving in loose ends. Step-by-Step Instructions How To Crochet a Simple Flower - Absolute Beginners
Medium weight (Worsted/Aran) or light weight (DK) cotton yarn is ideal because it holds its shape well. How To Crochet a Simple Flower - Absolute Beginners