We look for green spots on the map, pack up the minivan and drive towards that spot. This is how we found Anderson Park in the Galleria area, on a school day afternoon.
We parked and waited a few minutes and finally saw people walking over from the cross fit gym across the street. Once we saw some traffic, and the park had some eyes watching over it, we got out to play. (I bet this place is hopping during little league games... but we ALWAYS look for parks with lots of people watching over the space.)