I'm a React Native Developer so my answer will be in that context.
Global Variables: I used to define at the very start of my career.
Arrow functions inside render method: For the first 4 months, I think. Then I had to implement a FlatList and optimizing it taught me a lot about rerendering.
Inline CSS: It's a good practice to define a StyleSheet outside the render method because it keeps taking memory on every rerender.
I used to write code with proper indentation and format then I enabled format code each save setting in VS Code and it's so much productive now.
Using for loops: Can't say it's a bad practice but using Array Higher-Order Functions like map and reduce is so much efficient and code is more readable too.
Using recursive functions everywhere: When I first learned Recursive, I started using it everywhere which is bad. If the stack is going to be large then it will take a huge amount of memory and you might run into stack overflow. It's important to know when to iterate and when to use recursion.
Yup, that's pretty much it.