Answer to this question is something many developers talk about, but still not easy to make a quick list of best practices.
I have classified best practices into 3 for myself, you may find it useful, too:
1- Development best practices such as naming, foldering, modeling etc. Mendix learning paths give great clues about his type of best practices. I also look at the applications I work on and build an understanding of "what to do's” and "what not to do's’.
2- Best practices about performance: Very important but not necessarily visible at first. I suggest you to read articles about this. It is not easy to just look at something in Mendix and understand the performance issues. It is more of reading and experiencing. Please see this article for later uses ;
3- Security related best practices: The best way is to read documentations on Mendix website.
Have a nice day,
The documentation really is the best place to learn this. These are the same standards and practices that all Mendix developers should be following.
Hope this helps.