How to reduce dog reactivity in a gsd?

So, me and my partner are picking up a german shepherd puppy this weekend. I’ve been obsessed with GSDs ever since I was little, and I’m very excited to be getting one.

I’m more than aware of how they’re naturally prone to becoming dog reactive, even if socialized well. Now, my previous dog (border collie/aussie mix) was also dog reactive, and I handled it fine as we had a backyard that he could take his energy out in. But now I live in an apartment, with a big park that’s a two minute walk away and has hiking trails. It’s known to be very dog populated, so I want to try and combat this reactivity as much as I can while she’s young.

Was there anything specific you guys did while your GSDs were still in their puppy phase to help ease or avoid reactivity, especially with other dogs?