I struggled with figuring out how to transfer my skills from paper and canvas to the smooth surface of the iPad until I started downloading sets of digital brushes created by fellow artists. (Check out the extend list of what I use here)
Crayon Procreate Brush Pack* via Creative Market
While I do use almost all of the brushes for random shading, the first two brushes in the pack are my most used. I added the below reference on how the brushes look at their full size directly on my canvas.
*affiliate links are included