46 karma · joined December 4, 2018
The last dude is TheCherno https://www.youtube.com/user/TheChernoProject/playlists?app=...
All three of these folks walk you through intermediate-level projects with commentary on their decisions.
You should also look into conference talks on the tech stack you are interested in. Then look up the speaker/topic for more specific material.
More intermediate stuff goes into the data structures and algorithms. https://sp19.datastructur.es/ ^UCB's Josh Hug is a good lecturer, also provides course textbook, hw, side projects.
For best practices, try to get the Head First Design Patterns PDF.
Common mistakes? Search for "Effective <whateverLanguage>" and you should find a PDF for whatever you're looking for.
Also, goalkicker.com has compiled a lot of intermediate stuff from scraping StackOverflow question-answers.