4 low and first itd skid before itd crank over the engine. turn your wheels all the way one direction before you get out also. i do that even with a working parking brake and manual trans on the ramp in my truck. ive seen parking brakes slip and a brand new truck go glub glub before.
might throw some wheel chocks in the back too just for good measure (depending on how paranoid you are.
'90 YJ, ford 8.8, SOA, lincoln front, aussie rear, 4.88s, swampers.