That reasource is called experience.
Open the Ada Reference Manual, focusing on the Ada.* library pages, and write some packages for your area of interest.
Ben-Ari’s Ada for Software Engineers has some practice problems (the first edition is available online; you can get the second from a library - under no circumstance think of paying for it to the extortionist Springer racket).
Ada is an eminently readable language so you can simply read good code like
or
or really anything found on Alire.