You need to teach three things as priorities: movement and its associated modifiers, weapons fire and its modifiers, and heat. That might be easier if you take it in stages, such as letting him run a heat-neutral design for his first foray into the game, with a limited selection of weapon types to minimize confusion. Don't use something with extreme movement, but fast enough to get modifiers that can outweigh the penalties for moving. 5/8 might be ideal for that. Once he's familiar with getting movement modifiers and calculating to-hit odds over the course of several games, then you can introduce heat, jump capability, and other concepts. Somewhere along the line, play out an extreme movement versus extreme firepower scenario (such as Locust versus Panther), to show the plusses and minuses of each style of play, and how each 'Mech needs to be run differently for best results.