Sit down with your parent to discuss which powers your parent wishes to grant you.
Entitle the document granting power of attorney "Power of Attorney" to head off possible legal disputes over its purpose.
Insert any statutory wording required by state law. Pennsylvania, for example, requires the inclusion of the exact wording of the relevant portion of its power of attorney statute if certain types of powers are granted.
Identify your parent by his full legal name; state that he is the principal who is granting the powers. State that the principal is appointing you as his agent or attorney-in-fact -- these two terms are interchangeable. Your parent may appoint more than one agent if he so desires, but an agent must be at least 18 years old and mentally competent.
State whether or not the power of attorney is "durable." A durable power of attorney remains in effect while the principal is incompetent. If you skip this step, state law will apply a presumption as to its durability. Different states apply different presumptions -- some states will assume that it is durable, while some states will assume that it is not.
List the powers that your parent is granting you. Be specific enough to avoid ambiguity, but state the powers broadly enough to accomplish their intended purpose. For example, a power of attorney might authorize you to "select among available medical treatments or refuse treatment altogether."
Draft wording that clarifies when your authority begins and ends. You may include specific dates or specific events. The authority of an agent under a "springing" power of attorney begins only when the principal becomes incompetent; it usually lapses whenever the principal regains competence.
Sign and date the power of attorney along with the principal and any co-agents. Some states require signatures to be attested by a notary public, while others require the presence of witnesses who must also sign the document. All signing parties should sign in the presence of the others.