We simply let them go in the bathroom with their dad. They saw what daddy did and they did it. I tried the cheerios in the toilet thing, but my boys never (and still don't) had much of a desire to practice aiming.
I'm a single mom with a 3 year old little boy. Honestly, I didn't. He was still sitting down and his daycare teachers (all female) taught him. I'm not sure exactly what they did but I do know that they explained that girls sit down and boys stand up. I have however been working with him on making sure he holds himself so he doesn't pee all over the place. He had a really good hang of potty training before he was introduced to peeing standing up tho.