In which country and in which language and in which field would you like to improve?
In some languages you will find specialized books on specific fields of interest, like some very advanced illustration books in Japanese or Korean or some fashion design books in e.g. English and German.
Also there are a couple of trainings available in several languages via LinkedIn Training.
Adobe Illustrator CC is an essential design tool for anyone who needs to express ideas visually in print, on the web, and in any other medium. you will learn the basics of working with Illustrator CC so that you can incorporate visual effects into your workflow.