Use a lifting strap that wrap around the mast and pass both ends through a loop tied in the end of a line. For a single spreader rig the loop is run up to a few inches below the spreaders and the line is then tensioned and secured to a winch or cleat at the base of the mast. Front/back of the mast depends on radar/no radar. I have seen both with back of the mast most common. For my deck stepped spars that mast is lifted and set on the step. The uppers are attached, then the forestay and the back stay last