I leash them and make them walk around, and make a point to walk by their favorite potty spots. I also teach them a word that means "go now if you're going!".
Usually it's "outside"... so we can be tsanding in the lawn, I can tell goofy dog to go "outside!" he pees, and back in we go. Helps when they get older too, as you can ask them "outside?" and they either start to dance or ignore me entirely.
A small pup, if she doesn't go, I'd bring her in, watch her like nobody's business for any sniffing/circling, and immediately scoop her up and run her out, saying whatever word you choose to mean potty.
Lots of praise for going outside, and bits of treat for the foundling lab puppy who could care less about praise, but FOOD, well now...