We let our son figure things out on his own. We would put him down for a nap, and not go back in until at least an hour later. If he was sleeping, we'd leave him be. If he was awake, we'd take him out and try again later.
We gave DS plenty of time to practice going from standing to sitting during his awake hours so that if he stood in the crib, he wouldn't be "stuck" there screaming for help.
However, it has also been taking our son longer to fall asleep this past week, so I'm wondering if he's ready to drop a nap. Our son is almost 11 months.