As a few people mentioned finding "vertical" on the bike and using someone else to spot for them, here's my way, which a few people aluded to, so I'm not taking credit, just spelling it out in more detail.
I usually put down the side stand, then get off the bike. That way, if I have a clumsy moment, it lands on the sidestand, but I don't actually plan to use it.
Off the bike, leaning it towards me slightly, but definitely, I push down on the center stand pedal until the first contact with the ground. That's the pad NEAR me touching the ground.
Now, lightly holding down the pedal so the pad near me stays on the ground, I start tipping the bike away from me until I feel the SECOND pad hit the ground -- the pad away from me. You will know. As both pads are now on the ground, the bike is perfectly upright, and I know it. At this point, I put my weight on the pedal -- pause, realize I've got my toes on it again, and reposition it so my heel is on the pedal, and put my weight into it for real -- up (s)he goes.
Someone, sometime back, mentioned getting the bike on the center stand while SITTING ON THE BIKE (no boards, etc.). I want to see this.