You need to trust them and they need to trust you.You need to share, do pinky promise that you will share with each other because it's very good side of friend. Do your homework together! You will help each other with themes that you didn't understand. Show your respect, kindness, caring to each other. Just enjoy that you have each other! Play together, talk together and your friendship will be very long!
Never ever shout at each other because shouting don't solve the problem! Don't ignore each other, even maybe your best friend or you are angry at each other, but still say sorry! Do not be angry because your friend just talk with another person, because if you won't give him freedom he wouldn't like to be friends with you! Because he need to talk with another friends too! My last advice never ever lie to each other, cause lie is a start of break up!