Well, you could use independent grips for each finger and the thumb that correspond to the position of the mech's fingers. Some concept have proposed gloves that would detected the position of the fingers and translate those to the mech, also allowing more precise arm control. The legs would most likely have to be some manner of pedal system that translate specific presses and the pressure on them to how the legs should function. That is if you go with the more anthropomorphized mechs of Eastern design. Western designed mechs typically do not have as much fluidity of movement and are usually designed to look more like an actual vehicle, and often have integrated weaponry. With those mechs, it would actually be simple, and could potentially boil down to little more than a glorified console controller.
On this Mad Cat, for instance, it would actually be operated on basically tank controls, since the body turns independent of the legs. Weapons would be relegated to various buttons and triggers on the controller. It would actually be a very simplistic control method, compared to have the complex and difficult mechanisms needed for something like a Gundam or the others.
Actually, BattleTech's mechs use a neural interface that monitor's the pilot's sense of balance for steering as well as a few other things, torso twist and arms are controlled with a joystick, with another joystick for throttle, some mechs let you use the second joystick to move the arms and torso independently of each other too. Inner Sphere toads use mechs with fingers and those have a second control mode for using the hands.
Everything else, including all the fine movements needed to not trip over rubble or slide when turning at speed is automated, unless the pilot's sense of balance is telling the mech otherwise, which is why mech pilots need a lot of training so they know how to throw a mech off balance to lunge or dodge, not accidentally tell the mech to swing it's arms through a building while trying to aim at something.