I'm a big guy (~165 pounds when fit) and I land hard with each step. I have been running 70-100mpw in the summers and 50-70mpw during the school year but would really like to improve my mechanics. Are there any good sources of information on how to improve them? What are they?
land with your foot under your hip with your leg relatively (though not completely) straight. bring your heels under your butt and move them forward.
Search for various plyometric drills. Train like a sprinter.
Double leg hops, single leg hops, jumps onto a box of various heights, depth jumps from a box of various heights, various running drills, weight training, power exercises, etc, etc, etc,
Decent resources for various exercises: