i love mechs and (tried) to make a lot in maya. May i suggest you sketch out the general overall design of the mech. Then sketch out each piece by itself(to see how they will form together later), and make sure you add mech like details to help bring out the design like vents, hoses, cables, pistons(i see on hydraulic on on the back of the calf is a good start), and gears, pulleys... anything mechanical.
But it really helps to get the best visulization of how you want it to look as soon into the project as you can.