Unless you’re interested in a specific style of illustration already, I’d recommend practicing some basic techniques and then getting some sketchbook miles in. 

You’ll be better off to explore in advance then figure out what direction to study. 

Get started regardless. Daily practice starts with a 5 minute commitment then see how things unfold. 

 Yea the Udemy course starts with shading techniques and then basic shapes and then drawing simple objects using the learned techniques.