Understand the Business.
Go out of your way to understand the business side of your company. Analyze the business, product and service strategies, primary customers, top competitors, department relationships, and business processes.

Communicate Clearly.
Stay away from technical jargon and acronyms. Speak the language of the business, in terms they understand. Become part of the team instead of sounding like an outsider.

Justification.
Justify projects based on cost savings, improved market share, and revenue generation. These "value" statements are meaningful to top management and business units.

Follow Through.
When replacing legacy systems, don't forget to plan the decommission of the old system and follow through with that plan.

Treat Users Like a Customer.
Many IT professionals do not interact with their users. When they do, the treatment is terrible. All IT users should be treated as business customers. Understand their needs, expectations, concerns, etc. Listen first, provide them with the best solution alternatives, and most important, treat them like someone special.

Politics.
Remain neutral in all internal political battles. Never take sides.

Provide The Best Solution.
Always recommend the best solution to solve the business problem. Never recommend sexy, leading edge technology that would be fun to work with, and great for your career, but not solve the business problem.

Set Expectations.
Set appropriate expectations when new technologies are being discussed. Silver bullets and solutions that solve all your problems do not exist. Layout the advantages and disadvantages for all proposed solutions.