Since 1979, I have written professionally for a long list of businesses, non-profits, government agencies, and individuals.
What all these years in business have taught me is that one of the most crucial business skills is maintaining a rigorous sense of humor. I try to keep mine turned on while I do business. I've also learned that arguing with customers is a poor use of time, so I avoid that. Additionally, I learned that sharing credit when things go well and accepting responsibility when they don't will always pay off in the long run.
In fact, I've learned a lot of things that my customers find useful. Too many to list here, but give me a call (free of charge!) and I'll be glad to share the best ones.