IANAL, and what follows is emphatically not to be construed as legal advice.
That said, however, there seems to be a standard format for wills which, when properly composed and executed (see Cliffy’s post for important standards on execution), will result in a will that has a good chance of holding up in court.
First, you direct that your just debts and funeral expenses be paid.
Then you name someone (which can be a corporate body) whose job it is to make sure that your will is carried out as you specify. In most jurisdictions, that person is your executor, but some places have unique terminology. It’s wise to name one or more additional people as fallbacks in case your named executor dies, develops senility, goes into an irreversible coma, or some other unlikely but possible event that keeps him or her from serving as executor – or if he or she just plain refuses.
Next few clauses leave specific bequests to people. This can be Eve’s 1930’s style death telephone or great-grandma’s heirloom afghan, or it can be “I leave $5,000 to my good friend Albert Glock.”
Final clause tells the executor what to do with your residual estate – what’s left over after debts are paid and specific bequests have been distributed. This can go to one person or be divided in the ratio you set among two or more persons.
Each clause should say what happens if the person named predeceases you – does it go to their wife or kid, return to the residual estate, or what? Also take into account that you and that person might die at approximately the same time. Contingent heirs, beneficiaries, etc., should be named.
You should be aware of what your state’s laws on stuff like dower and curtesy are – under North Carolina law, half my estate must go to my wife if she survives me, or she can challenge and defeat my will. (As it happens, she gets everything if she outlives me – but it’s necessary to be aware of what the law says on things like that.)
In the event that you disinherit or leave a very small bequest to a relative, it’s important to state why. E.g., “I leave the sum of $100,000 each to my son Marvin and my daughter Earlene, to be distributed per stirpes to the heirs of their bodies if either predeceases me. Because I have given a like sum during my lifetime to my son Harold to finance his successful used-snowmobile dealership, I am not making a similar bequest to him. But he remains my beloved son, and I do leave him my collection of antique blunderbusses.” Or “I leave my residuary estate to be distributed equally among my three children. Because my wife is the sole beneficiary of my $5,000,000 life insurance, I do not provide separately for her in this will, other than the clauses above leaving specific property to her.”
Two apparently contradictory propositions govern wills. First, because you’re not available to answer questions (at least not without a séance), your will should reflect clear statements of your intent. Brief and explicit is the rule. However, for precisely the same reason, you should go into as much detail as is necessary to make crystal clear what your intent is. “I leave to John Smith my 10,000 shares of I.B.M. stock” may reflect your intent to remember your college roommate, but “I leave my 10,000 shares of I.B.M. stock to John Montmorency Smith, my former college roommate, who resides as of the writing of this will at 1403 Old Wertsboro Turnpike, Grommetsburg, Rhode Island” means that every John Smith you’ve ever met cannot sue your estate for that stock.