Acquaintances to Friends?

At the moment, I'm having some trouble realistically developing a relationship between my two main characters after they're first introduced to one another (both male teens). I want to make sure the (relatively swift) transition from acquaintances to friends remains believable, whilst avoiding sluggish dialogue between the characters - after all, they are meant to instantly get along... but again, it's finding the right balance I'm struggling with.

Do you have any pointers? All help is greatly appreciated!

What do they share? I've made most of my friends when we're working towards common goals. We talk about work, mostly, then we get into our personal lives outside of work/anything stopping us from work, which leads to being friends.

Is one of them in trouble? Another way I've made friends. One comes to help me out and we get to talking.

How similar are they? Both in activities and values they hold. You can have total opposites in personality but they have similar morals and ways they go about expressing them. Do they enjoy the same activities and get to talking that way?

Have them do stuff together and show how they just seem to click will help a lot. Having them enjoying each other's company will also help a lot.

Thanks for taking the time to reply. I think I know where I'm going now