I always make sure my beer and lemonade are both ice-cold before I even think about mixing. A shandy made with room-temperature ingredients just doesn't hit the same way. I pop both in the fridge for at least an hour ahead of time, or I use a quick ice bath if I'm in a hurry.
I fill my pint glass about a third of the way with ice cubes. This keeps the drink cold as I sip without making me wait for a separate chilling step. I try not to overdo the ice, though, since too much can dilute the flavor quickly.
I pour the lemonade into the glass first, right over the ice. Starting with the lemonade helps the flavors blend more evenly once the beer goes in, and I find it reduces excess foam compared to adding beer first.
I slowly pour the chilled lager over the lemonade, tilting my glass slightly like I'm pouring any beer to control the head. This is the moment the drink really comes together, and the aroma alone tells me I did it right.
I give it one or two gentle stirs with a long spoon, just enough to combine without flattening the fizz. Then I drop in a lemon slice and a sprig of mint if I'm feeling fancy. At this point, it's ready to drink immediately.