So I'm fairly new at domotics, I've been introduced to it by installing Plug&Play devices.
In my life I've heard that the best way to get things right is by knowing how to get things wrong, therefor comes the question;
What are the most common issues that you guys stumble upon?
Just look around and you see a lot of issues that people stumble upon.
It just all depends on current knowledge, your ability to grasp/learn and drive to get into HA.
Here you go. These are the first 4 I found using the forum search. You'll probably find more similar topics if you search for "wish I'd known"
Also, the Cookbook section of the forums is a great collection of resources which usually tends to be overlooked. You can find it here The Home Assistant Cookbook - Index
Please don't. I have been using Home Assistant since before Lovelace, and until this post, I had never heard of "domotics". We don't need yet another term that adds nothing to the conversation.
For me it was and is the python-esc coding style. Indentations are important. The documentation has code snippets, but when creating those snippets in my own code, I never knew how far the snippet has to be indented. To add to the frustration, I have found indentation errors in the documentation. Fortunately, at the bottom of each document is a place for feedback where one can make suggestions for improvement.
templates/JSON//Jinja make the code more robust but make the learning curve even steeper.
The links provided by shadowfist are actually a must read before you venture into HA