Here is my list of heuristics and rules of thumb for software development that I have found useful over the years:
1. Start small, then extend. Whether creating a new system, or adding a feature to an existing system, I always start by making a very simple version with almost none of the required functionality. Then I extend the solution step by step, until it does what it is supposed to. I have never been able to plan everything out in detail from the beginning. Instead, I learn as I go along, and this newly discovered information gets used in the solution.
I like this quote from John Gall: “A complex system that works is invariably found to have evolved from a simple system that worked.”