what part of the body makes the most sense to start on

6 jackstands; 2 on k member, 2 at front rear spring mounts, 2 at rear bumper crossmember, leveled side to side, and lengthways by door sill. Then re-check door fitment.

and if you plan on doing more; plumb bob down, and mark floor, so you can pull the rearend back to square, if installing diff suspension.