It’s recommended to brush your teeth twice a day for two minutes each session. Another basic rule is to replace your toothbrush after every three or four months. When you brush your teeth, there are specific rules to ensure an effective and safe clean such as adjusting your toothbrush at a 45 degree to your gums and gently brushing back and forth.
For a full step-by-step list on brushing your teeth, read this article!