Try these steps for yourself, even if you already have an advance directive. See the attached resource list for forms. This helps you see the variations in topics different advance directives cover and the alternative instructions they provide. The form-publishing business may be burgeoning, but most are inadequate in one respect or another. Even with the best drafting, there is no perfect form for everyone.
People are different.
Second, discuss the contents of the forms with your physician, close family, and the person you may name as proxy. Most people find these discussions difficult to initiate, but they are extremely important. Third, complete the form you choose, being sure to add or modify language to reflect your wishes more accurately. Be sure to follow the witnessing instructions for your state exactly. Most, but not all states, require two completely disinterested witnesses.