Talk to the person you want to name executor. Confirm that she understands what an executor does and what her responsibilities will be. Tell her where you are storing your will, so she doesn't have trouble finding the document when you die.
Name the person you chose as the executor in the appointment or naming section of the will. Write in her full legal name where indicated if you're using a will form. Don't use nicknames.
Use state-required wording for nominating an executor if you're writing the will yourself. Wording differs by state; check the official website of your county's probate or surrogate's court to find state laws regarding executor nomination wording in a will. An example of a common acceptable phrasing is, "I hereby name, appoint and constitute (executor's name here) as the executor of my Last Will and Testament."
Complete your will. Both you and at least one witness over 18 need to sign the will. State laws vary on how many witnesses you need. Check with the county probate court for laws relating to proper final will execution.
Store the will in the spot you told the executor. Tell your executor if you change the will's location later.