Know your limits. Accountants should understand the limitations oftheir expertise. Just as your family doctor should not attempt a heart transplant or brain surgery, tax professionals have a much better grasp of tax law. If you're the tax director of a US-based company opening a new subsidiary in Italy, the fact is that you know next to nothing about Italian tax law. There are so many facets of a wide variety of different taxes (income, sales, property, business, payroll, etc) that are specific to the geography in which you business. Know your limitations and when to seek help from those experts which deal with these issues for a living.
Keep good records. Sooner or later, you'll probably be audited in some tax capacity. Keep meticulous accounting records on the supporting documentation for your tax filings. For every item you can't prove, this may translate to unnecessary tax dollars spent by your business. It's fair to say you'll be fired, when the CEO is forced to sign a big back tax, interest and penalty check which is due to your negligence.
File returns on time. This should go without saying, but if you're ever backlogged, tax returns should not get placed on the back burner. Most tax jurisdictions have penalties and interest associated with the non-timely