I've always used the spin halyard attached to the bridle. I've done it for years and never had it go wrong.

With the mast down and shrouds attached properly, run the spin halyard to one of the bridle tangs on a hull. Temporarily attach the forestay somewhere convenient on the mast (I use the gooseneck). Now lift the mast to vertical and, once there, take up all the spin halyard slack and cleat it. Your mast will stay up while you step off the tramp and rig the forestay properly.