Optimization

"Premature optimization is the root of all evil."
Donald Knuth

No need to say more...

UnderstandingThe Domain

Sysyem metaphor is a very important practice. Understanding domain and implementing model for this domain is key to success and good software. If the developer does not understand the doiman clearly; only algorithm or steps of the process and does not focus on "why" and "how" the process is going on, he/she builds the domain model incomplete, give irrelevant names to the entities...etc. And it becomes very hard to understand the code targetting the domian

So, th domain should be understood clearly, and the common vocabulary for the domain should be developed and team should be careful about this.