Just 5 states don’t impose state sales taxes: Alaska, Delaware, Montana, New Hampshire, and Oregon. However, that doesn’t keep them from charging income tax, excise taxes or tourist taxes. And it doesn’t mean that cities or municipalities within those states can’t change a local sales tax.

There are complicated rules for how stock-option taxes are calculated, sometimes depending on whether the options the employer granted are statutory stock options—granted under an employee stock purchase plan or an incentive stock option (ISO)  plan—or nonstatutory ones. ISO options affect alternative minimum tax and nonstatutory options have three possible tax events, so get the help of a tax advisor to handle stock options issues.

Documents around property acquisition and improvements are especially important for capital gains tax when you sell your home; so are documents needed by heirs to establish the cost basis of stocks they inherit.

Start by using the exclusion for $250,000 of capital gains ($500,000) for married couples if the home was your primary residence for at least two of the last five years. Then look at all the expenditures you made that can reduce the amount of capital gains—for example, capital improvements, settlement fees and closing costs.

 Alternative minimum tax (AMT) is a system invented to make sure that higher income people with significant tax deductions didn’t avoid paying federal income tax. It uses a separate set of rules to calculate the tax owed after adding certain tax preference items back into adjusted gross income (AGI).  What you need to do is keep your AGI as low as possible through maximizing salary deferrals and pre-tax contributions to flexible spending plans and the like, keeping tax-efficient investments in taxable investment accounts, and taking all the tax credits of which you qualify.

Some of these are simple carelessness, such as using the wrong line of the form or entering incorrect figures or names. Others are automatically taking the standard deduction, missing write-offs, making math errors, not telling the IRS what to do with your refund, and making payment mistakes.