Stromovka Park
Walk around Stromovka park on the north side of Prague. It's a beautiful managed forest, the old royal hunting grounds. It's full of trees, ponds, flowers, mallard ducks, and locals strolling with dogs and children. I didn't see a single tourist (in May).
North of the park is a small island with an equestrian center, cross over the island into Troja, double back on the road to the east of the bridge, look for a little road called Povltavska. Have a nice drink and snack at Cafe U Lavky, owned by a very friendly German woman named Zdena.
Letna Park
Another nice spot with no other tourists spotted. Mostly local dog-walkers and joggers walking through this park that parallels the Vltava on the north side of the river. There's a nice beer garden where you can pause and share a pivo with the locals.