I have a yard crane so can lift the mower up vertical if I want
However when I am doing multiple mowers simultaneously I do use jacks
For ZTR's drive it backwards just a little to turn the caster wheels into the reverse position ( or turn them by hand )
place some car or truck ramps behind the read wheels & drive the mower up onto them.
That should be all you need to do & will leave the mower very stable
IF you really need to the front can be lifted by hand and jack stands placed under the frame front cross member , not the caster wheels but you will need truck or SUV ones as most car ones are too short .
When you have finished remember to turn the front casters to the forward position before you drive / push it off the ramps or you risk it running off the side of one of the ramps .