First try the strategies outlined in the article titled Well Behaved Children. Try them for two weeks, so your young one can get used to the "New You."
This is a saying which I borrowed from teachers. For example, if the child forgets to act horrible, you compliment them on behaviors that you like to see, like taking the plate back to the sink, putting cup on the counter instead of throwing it on the floor, picking up a toy, or avoiding foul language. If a child is picking up the toy to throw it, you can interrupt the flow of motion by grabbing the toy and saying, "Great picking up!" Remember to gossip to grandma or a friend on the phone about how your young one is acting older everyday and how proud you are of them.
If the young children are surrounded by adults and adult conversation, they will be bored and feel left out. They will try to be cute. If that does not get them attention, they will spill things, eat like a dog, refuse to eat etc.
The remedy for that is to remember to include them in the conversation by telling the others about the child's accomplishments, and new skills. If the child likes to talk, ask them questions about their favorite topics. When the adults are talking, maintain occasional eye contact with the child, and smile at them when they are behaving well.
Give it at least two weeks for your young one to figure out that it is the same system. If it seems like a lot of work, do it anyhow. If it works, it will be worth every minute of your time.
By 18 months, every self-respecting baby can tell who is the family is "the easy touch". As the children get older, they will learn to manipulate. This is known as the game of LET'S YOU AND HIM FIGHT and I'll just slip away and do what I want. If you fall for this trick, you will have a hard time controlling the situation and your family life will be in constant uproar just because you one wanted to do something that you did not want something that you thought was a bad idea. The remedy for that is to get all the adults in the immediate family together and decide on a single course of action. The best TIP I can give you is to ALWAYS GO WITH THE STRICTEST DECISION. Your young one will fume, but they will be glad to have a clear direction so they tell their friends "no go".
When setting up consequences, start with the positive ones for good behavior. Keep track of the child's progress on a calendar, which the child can view easily. Decide with the child, what the rewards should be - whether to use point system or stars. How the accumulated positives can be exchanged for toys or other special treats. The negative consequences can be having points take away or pictures of clouds. When it comes to rewards, only stars can be exchanged for toys or money.
There should be consequences for disobedience and bad behavior. For very little ones, you just take their hands to stop them and say "No" sternly and make a mad face (even if you are laughing inside).
Two year olds love to test limits. Most of the time it looks very cute, but you want to train them that when you say "No!" really loud to stop in their tracks. The do not know enough about the world and could easily wander out into the street and get run over, or stick their fingers in the shredder etc.
At age 3, you can start little timeouts of 3 minutes, to give them a cooling off period. Set timeouts by age, so for a 10 year old you would use 10 minutes. Do not use the timeouts to give yourself a break from the kids.
With older kids, the consequences have to be something that they care about. For example, you would not give a timeout to a child in his room, if he prefers to be by himself. That would not be punishment for that child. Your children will go through phases where their phone, computer, IPOD, cell phone, bike, or car is the most important thing in their life. Make the punishment fit the misbehavior if it was a serious infraction of your rules.
Post the rules on the refrigerator, after you make sure that all the adults in the house agree to them. This way your children cannot claim ignorance.
If the misbehavior was horrendous and you feel really upset or really mad, give yourself a cooling off period. Do not mention the behavior even if it takes you a week to cool off. The child will sense that something is up and will worry. They will also know what they did wrong and will worry that you found out. Let them worry. You take that time to strategize, on how you will handle the situation and what punishment is fitting. By then you will have gotten over the impulse to send them to a monastery in China, or to your grandparents' farm, or to a private school which you may not afford.
Once you decide on a punishment stick to it. Do not change it because it is inconvenient to you, the school or your other family members. That is why you want to think about punishments, you want them to be a lesson for your young ones - not something that will create a friction for everyone else in the family.