• Make time for your friends and be a good listener, offering advice and support when needed
• Be trustworthy and keep your promises and secrets as best you can
• Apologise if you have made a mistake. Remember, not everyone is perfect, and mistakes happen, so be willing to work through any disagreements or arguments
• Just be yourself and accept your friend for who they are
• Be respectful of your friends’ opinions, beliefs or feelings
• Encourage and support your friend, and help them grow as a person
• Look out for them even if it means getting support from others to help keep them safe. This might be difficult to do, and your friend may not like it at the time, but they will be grateful of your support later on

Remember: Good friendships can help in many ways, from improving your mood to supporting you through difficult times and everything in between. Some friendships will last longer than others, but all friendships play an important part in your life.

(Source https://www.healthforteens.co.uk/relationships/friendships/friendship-just-the-facts/) 

Sometimes friendships have problems, it can be hard to know what to do. Childline lots of advice about things like falling out with friends, fancying a friend, missing a friend or being bullied by friends. 

https://www.childline.org.uk/info-advice/friends-relationships-sex/friends/friendships/