Put 40-50 pounds in the tires and find a flat smooth empty parking lot. Put the seat down low enough that both feet touch the ground. Propel yourself forward with your feet for a while until that feels OK. Lift your feet onto the pedals and coast for a while. Then raise the seat enough so that you can pedal. Just stay in that flat smooth empty parking lot until it feels OK to ride.

On the other hand, 10-15 pounds of air may have been your major problem - that could cause things to feel not right at all. Airing up the tires might be all you need to get going. Find a good place, as above, to practice, though.