I didn't get that much things in common in the beginning, except that we would understand and laugh from the same jokes. It took a while to refine many other things, like understanding things without needing to say and so on.

You have to have things in common to be a resting place, so that you have peace of mind while doing those things together.

You also have to have things that you're good at and that makes the other person proud (kind of envy) of you, things that they'll contemplate while you're doing.

And, finally, things that you suck at but they are good, so that you'll also stare while they are doing and will keep you enchanted.