1. Be honest
Let say if you ask your friend opinion, they will give it honestly but gently. Your friend might not always tell you what you want to hear , but at least they say the truth, they'd be honest.
2. Always be there
Always be with friend who needs you. Listen to what they want telling you. Be a good listener!
3. Be respectful
Always respect your friend. Respect their opinion even you don't agree with his/her opinion.
4. Give your friend space
Understand if your friend wants to be alone. Maybe they have some problem that can't be share with you.
5. Don't be selfish
If your friend needs your help, help them. Don't be selfish! Who knows , one day, if you needs help, they'll help you.
Let's be a good friend !