Use water that's as close to seawater as it can be — extremely salty or, better yet, seawater itself. And don't use much: Put three or four inches in the pot, and when the water is steaming like mad, add the lobster.
A pound-and-a-quarter lobster takes about nine minutes. Afterward, don't shock it in ice water. That makes the meat tougher. Just let it cool down.