1. Ask the child nicely to do something that you need them to do. Do not command. Commands will make them feel like rebelling. You will be suprised how much asking them will work.
2. If the child doesn't listen, see if there are obstacles such as hunger, being overwhelmed, distracted, or tiredness that are inhibiting their obedience. If so, take care of that first, if not...
3. Tell them you will help them to obey, and physically go over and help them to do what you ask. Do not get angry, just cheerfully help them.
4. If they still will not obey, then you can use the 123 magic method which is where you count to three and if they are still not obeying on three you give them a logical consequence (without anger) that the child will care about. (You must ALWAYS give the consequence if you get to count three, otherwise it won't work and the child will test you to see if you are serious all the time).
This method really works, and if you are very consistent, and using the love languages too, you will have to get to step four less and less over time.
It is very important though that children learn to obey....the younger you teach them, the easier it will be for you and them. Also when children can control their bodies and make themselves obey, they will have more self-esteem, and learn how to function well in society and in school. So this is one of the MOST important skills you will teach your child.