It all depends on the action and how many bullets you want to shoot. As already mentioned, sighting through the bore is an excellent way to get on the paper with bolt actions. For actions where removing the bolt and sighting through the bore is not possible, auto, pumps, and lever actions, I like the SL-100 Mag Laser Boresighter.
When mounting scopes I use Blue Loctite, Wheeler "Fat Wrench" for torquing screws, and ring lapping tools and abrasives. I feel that lapping the rings helps relieve scope tube stress and adds holding power by creating more scope ring surface that contacts the scope.