Different rules and programming methods are needed based on the hardware and software being used. Programming in a Siemens programmable logic controller (PLC) is not identical to programming in an Allen-Bradley PLC. There are general good practices that should be followed in any programming. The obvious is to have the program function and control as desired. Maintaining good documentation and housekeeping are good general practices in programming. Code should be easily read and understood by programming colleagues and customers. Poor documentation and housekeeping can add unnecessary time to troubleshooting, downtime, and programming. Programming structure and how complicated it may or may not be is another variable that will affect how easily the code is deciphered. I suggest following the KISS principle: “Keep it simple, stupid.” Avoid unnecessary complexity and keep it simple and straightforward.

Good rule to follow.

Indeed it is much easier to work with a well documented program. Specially when troubleshooting and the program´s author is not reachable.
It begins with the organization of the program itself, and involve information notes to help people to understand why things were done that way.
But sometimes I think professionals don´t document programs intentionally, trying to keep costumers attached to them...

True that. I have that same feeling.

Agreed...and no fancy tricks.
I was once asked to look at a program that was written by some one who was no longer on the plant site. The company had tried to make some changes for years and every time they did it screwed everything up. It was a Modicon system and after a few minutes of looking over the calcs he had written, it dawned on me. Most manufacturers scan across the page from left to right and then down the page jts as if you were reading a book. Modicon scans up and down and then moves across the page left to right. He had written all the calcs using the up and down scan. Efficient, but confusing to some one who didn't understand exactly how the machine worked.

Yes a structured & commented program is always easy to troubleshoot and maintain. Ease in understanding. But PLC memory space is less and without a memory card a small PLC always comes without comments.

True. However, with a smaller PLC with lack of memory space, printed documentation becomes all the more important.

I suppose the main thing that we all agree on is to keep your programs readable, understandable for everyone and document everything you do.