First, for a good basic primer on Twine 2 and SugarCube 2 see "A Quick Twine (2.2+) Tutorial". It gets a few minor details wrong, but the majority of it is correct.
Then the next best thing to do is start by reading (or at least skimming) through the SugarCube documentation and the Twine wiki just so you get an idea of what all they can do for you, and keep those links as a reference.
Also, be aware that you can open any Twine game in Twine to take a look at the code in it to see how other people did things (you'll need Twine 1 to open Twine 1 games, and Twine 2 to open Twine 2 games). So if you've seen something neat in one Twine game, you can import it into Twine to take a look at it yourself and see exactly how it's doing that. (Remember, "To steal from one source is plagarism. To steal from many sources is research." ;-) )
If you get stuck, there's this Twine Q&A site, the r/twinegames subreddit, and the Twine Discord server with plenty of helpful people (though be patient, as not all questions are answered immediately).
Hope that helps! :-)
EDIT: I can't believe I forgot this, but I also have a bunch of useful Twine 2/SugarCube 2 sample code here.