It is a big question with so much hard work. I sometimes prefer to call it as the "A following-up day by eagle eyes"
Here are my ten general strategies with students of grade 3, 4 and 5:
1. Must be started at the beginning of the school year. As early as you begin as early you reduce the rate of bullying.
2. Identify it clearly and explain the difference between other similar behaviours like being mean, unkind, confliction, etc.
3. During your school day, keep raising the pool of positive words in your student's dictionary. For example: instead of saying "You were rude to your friend" try to paraphrase it like "I was surprised to know that you were not nice to your best friend!"
4. Have a personality folder for each student. Study their character and focus on the students with challenging behaviours ones.
5. Build the students "Social skills", teach them when should say "Sorry" or "No!". How to act if someone pushed them or said something wrong. "Use your tongue before your hand or leg!" is my basic rule.
6. Always remember, when you deal with challenging behaviour child, your job is to save the remained positive character, not ruin the last chance to teach the child how should behave.
7. Separate between the challenging behaviour and child's character. Remind the child that the chosen behaviour was wrong but he/she is a good child.
8. Be ready to the difference between your educational method and child's parent one. Sometimes they encourage the rule "If someone hit you, then hit him/her harder!"
9. Keep talking to your children and be always available and visible. "I'm sure that you can make today better than yesterday.", "I trust you!" and "You already know the rules, right?" sentences like these could have magical effects.
10. Even if you are representing the discipline in your corridor, show the love to your students. They learn from their surrounded environment.
*All opinions are my own*