What kind of concepts are essential for an amateur-intermediate programmer to grasp and learn?

Question

By concepts I mean anything from OOP to algorithm complexity to multithreading... just anything you guys think can help any amateur programmer expand their knowledge. thanks! :)

Answer 1

Logic and Reasoning
Principles of Programming
A slight tad of Computer Organisation (about how bits and bytes work, CPU, memory, I/O, etc)
Discrete Mathematics
Algorithms for Programming
Some algebra

Answer 2

learn how algorithms work side by side with programing. it will help a lot to understand logical expression of a program.

Answer 3

algo behave like a structure of program // so ,must essential thing is only that how algorithm works ! and must be ensure about the steps of algorithm in step wise so code or program must be easily implement !!