Determine the powers that you wish to grant your agent. Very few people grant general powers of attorney. If you state your agent's authority too broadly, you run the risk that the agent will overstep the authority that you intended to grant him. If you state your agent's authority too narrowly, you run the risk that he will be unable to accomplish your intended purpose.
Search the website of your state government to find out if it offers a statutory power of attorney form. Many states require you to use a statutory form for certain purposes, while other states offer them as an optional convenience.
Research state law to determine how a power of attorney form must be witnessed. Many states require notarization, while other states allow one or more witnesses to be used instead of a notary public.
Entitle the authorization document "Power of Attorney", if you are not using a statutory form. Identify yourself by name, include a formal statement that you are mentally competent, specify the powers you wish to grant to your agent and identify your agent by name. Specify any beginning and ending dates that you want to use. Alternatively, you might use an event to trigger the power of attorney -- for example, a medical power of attorney, usually called a Durable Power of Attorney, might be triggered whenever you become incapacitated, and expire whenever you regain capacity.
Add signature lines for yourself, your agent and any required witnesses. Even if state law does not require your agent to sign the form, his signature provides evidence that he accepted his appointment.
Sign the form, date it and have your agent and witnesses do the same. Give the authorization form to your agent.