Keep calm: don't allow yourself to be seized by self-doubt! You are okay as you are.
Block those who annoy you: the majority of providers give the opportunity to block people who annoy you through settings. After that they cannot establish contact with you.
Don't answer: don't answer the messages of people who annoy you, because if you answer, the attackers will have confirmation that they are effective and things will likely get worse.
Reliable evidence: save everything that disturbs or hurts you, no matter if photos, video or messages, because it will make it easier to show others what happened. They can be used as evidence if you report the bullying.
Talk about it: when you have problems, get in touch with people who can help you, e.g. your parents, teachers and friends you can trust.
Report problems: don't leave this behind, but report to the operator of the network or the police if you think it could be illegal.
Support the victim: if you notice that somebody is being bullied by someone, help them! Talk to the culprit: when they notices that the victim is not alone, they often stop the bullying.
Protect your private environment: be careful about what you post on the internet. Personal data such as address, e-mail, telephone number could be easily used against you.
Know your rights: nobody has the right to post your photos or videos on the Internet, nor to defame or insult you. When cyberbullying becomes particularly serious, this can have legal consequences for the perpetrator.
Believe in yourself: it is important to believe in yourself. Don't let anybody ruin your life and don't ruin anybody's life.