Generally, it's a good idea to establish for your child that consequences exist, but you need to do so within reason. If your child has done a particular thing wrong for the first time, or they did something that was okay in one situation but wrong in this one, you should only give them a warning. They're learning and can't be expected to read your mind. However, if they repeat a behavior that they know isn't allowed, consequences should be put in place. Before imposing consequences, warn the child that consequences are about to happen. Counting to three is less ideal, since it teaches your child that they do not need to respond to your requests immediately. Instead, tell them that consequences will happen if they do that action and if they don't immediately stop, it's time to put those consequences into action. The consequences for an action should be proportionate, appropriate and logically related to the action your child took. You do not want your child to become confused about what they did wrong or why it's wrong. Match the consequences to their actions to help your child learn and keep you from over-reacting in frustration. For example, if your child throws their dinner when they're done eating, make them clean it up. However, if they refuse to eat their dinner, then just take it away and give them nothing (or a simple meal of whole grain or other healthy bread and a glass of water). If they are fighting over a toy, take the toy away for a period of time. If they refuse to put on a coat, simply let them be cold for a little while. Everyone in your child's life, including their mom, dad, grandma, grandpa, brothers, sisters, etc. all need to follow the same rules. All family members need to know that consequences need to be put in place if the child does something wrong. You don't want your toddler to become used to bad behaviors that they then bring back home or to other environments. This can be tough, but explain that it's better for everyone and help give them the tools they need to put consequences in place.

Summary:
Know when consequences are appropriate. Warn children of consequences. Match consequences to actions. Get everyone on board.