Collect all the funds necessary to purchase a cashier's check. Remember to have a bit extra to cover the transaction fee. These funds cannot be in the form of a personal check.
Research banks in your local area. Most major banks (Bank of America, Wells Fargo, Citibank) offer cashier's checks to the general public. You may run into trouble if you look only at small community banks and credit unions. Stick to large, national banks. Not only will you have better luck, but you'll likely pay less in transaction fees.
Think about how you will bring the money to the bank, especially if it is a large amount. You can purchase a lock-bag--a money-carrying bag that is only opened with your key. Another strategy is to make several trips and obtain several cashier's checks. This will increase the transaction fees, though.
Bring your funds, in cash, to the bank. Ask the teller for a cashier's check in the amount required. Typical transaction fees run between three and ten dollars. If the amount you are requesting is over $10,000, you may need to fill out an Anti-Money Laundering form. This is as a result of the U.S. Patriot Act.
Confirm the amount on the cashier's check. Do not endorse the check, if it is made out to you, until you are absolutely sure it will be cashed as you intend.