Soft Language -- Never use hard words like: always, very, never, extremely, or recommend. When necessary, it may potentially be beneficial to use words like: suggest, perhaps, potentially, sometimes, often and may.
We, Not I -- We are a team, and so anything we say in written or oral form must express that. The only time "I" is appropriate is when apologizing, because it was I who made the mistake, not the team.
Paradox of Pay & Value -- The minute you leave consulting for corporate, the value of your advice is cut in half but your pay will double.
You're The Expert -- Clients will look to you for advice and save emails that you send for years, going back to them when they forget.
Clients Come First -- They come before you, your family, and your sleep. They come before any internal projects. When in doubt, just make clients happy.
Beauracracy -- Unless you're at a boutique firm with less than 30 employees, there will always be beauracracy, layers of management, and inefficient administrative issues to content with regardless of what side of the relationship you live on.
Internalized Expertise -- Try writing down the process of tying your shoe and giving it to a child who doesn't yet know how. You've internalized tying that shoe and it's much easier for you to just do it than explain the thought process and algorithm for doing so. Experts in professional services are analagous. Just give them the keys and let them drive, don't make them explain how they drive, it's an inefficient use of time and money.
Storytelling -- It's a scientific fact that adults learn best through analogies, examples and storytelling. How much easier was it understanding point #7 above with the examples? Still think it's just a fad? You need look no further than Homer's Odyssey or Iliad.
People Run Businesses -- The classic thinking is that because it's a business and corporate, everyone must be buttoned up and serious all the time. Even in Board rooms of the largest companies on the planet, there is still friendly banter and relationships being established. People work for and with people, not faceless companies.
Change is Hard -- Regardless of the number of times you've experienced this fact and even internalized it, change will always be difficult for everyone (and yes, I'm using hard language). Whether it's a merger of equals or simply going with a new paper supplier, the devil you know is better than the devil you don't.