Look for a tutoring job. There are always students that need help, especially in spelling. Some of the rules are tough to master and it is straight memorization, which is difficult for many students.
Talk to your local school. Teachers know best who needs help in their classes. They may have already discussed getting a tutor with the parents. Therefore, they would be able to set up a meeting with you and the parents or give you the information you need to set up the meeting yourself.
Meet with the students. It would be preferable to meet with the students away from the school environment. You want to start with a bond between you and the student so you know how to relate to them. Each child is an individual and therefore has individual needs. You need to cater to the needs of each child that you tutor.
Set up a schedule. You want to be able to work with each child individually. Do not take on more students than you can handle. It will not help the children if you are spread too thin. Tutoring is a fine art, you need to be able to adjust to each child and give them the necessary information that they will need in a way that they can understand.
Cultivate patience and perseverance. These are necessary traits for any tutor. Your students are going to be contrary and you are going to have to be very creative to help the students learn to spell.