Let me ask you few basic questions before we start with one of the most important best practices required for a software developer.
Definitely your answer will be positive but if I ask you one more question in the series:
Only few software developers will have positive answer because reading and understanding an existing software source code is the most boring task. If you are one of them who feels reading software source code is a boring task, then you are missing one of the most important best practices, which a software developer should have in his/her life.
If you want to become a novelist, can you just start writing novels? I would say 100% no!!, you definitely need to read hundreds of novels before you start writing GOOD novels. If you want to become a movie script writer, can you start writing good movie scripts until you have gone through various good movie scripts?, again my answer would be no!!
So, if you want to write a good software code, then how it will be possible for you to write a good source code without reading tons of source codes? Even if you will write something, then how would you know which is the best?
Reading source code written by others gives you opportunity to criticize the mistakes done in writing that code. You will be able to identify the mistakes other software developers have done in their source code which you should not repeat.
There are many attributes of software codes (indentation, comments, history header, function structure, etc.), which you will learn by reading existing code, specially, a code written by well-experienced software developers. Spend some time in reading others' source code and I'm sure you would be able to write BEAUTIFUL source code in few days or few weeks and you will be able to fix the mistakes, which you were doing so far in writing the source code.
One thing to experiment, just go in the past and check the code you had written few years ago, you will definitely laugh....because you are always improving by doing practice.