The saxophone is a complex instrument and requires lots of focus and attention to detail to play well! The following books are all very good resources to help develop your knowledge of and ability to play the saxophone.
The Universal Method by Paul Deville is the best possible single book to get for any saxophone player. It’s HUGE and comprehensive.
These 25 exercises in the Klose book will take you through the entire natural range of the saxophone and help you develop speed and accuracy in fingering and articulation.