well I must say it very nice to inspire anything.
I can pretty much echo the advice given here already. The bots I did were really a practice in planning and using a logical process, and I think it was success in that goal that made them a success as peices.
I can certainly recommend before all else, taking a sheet of real paper and just doodling a few ideas, and getting a basic design in mind before making any pixels.
The beauty of working with something like a robot I guess is that the anatomy is all up to you, but its still a good idea to make sure it all makes sense, and think about his stance.
baccaman21's certainly right in saying you should initially aproach any complex iso work as a technical drawing.
As such I've made a quick image below to show how I might aproach planning your current design.
First of all draw some iso guidelines like I've done . You can do a few or make a whole grid. Remember lines in this isometric style go along two pixels for every pixel they move vertically - this ensures everything looks smooth and things line up nicely.
Take a different colour and just roughly sketch out your design. it will help a lot to draw what you wont see in the final image - see how Ive draw the back edge of the feet and the rear shoulder, and I've used coloured marks to plan where the joints will be. The lines dont have to be neat here but get your mesurements as accurate as posible.
One good general drawing tip is, if a line looks out of place, draw the replacement before erasing the wrong one.
Another thing to remember at this phase is, Isometric means "equal measure". Take this literally, it means there is no vanishing point, and assuming the stance is roughly semetrical, if one arm/leg/whatever is so many grid spaces high/wide, then so should the other.
for an example of this look at the knee caps below, see how they both line up to make each leg two grid spaces high, and one wide.
Once you have a basic drawing like this take another colour to draw your final lineart/outline over the top. obviously smooth out any lines, and if any lines can easily be converted to one of the 'perfect pixel' lines without distorting the proportions, do so.
Once thats done you can finally start thinking about lightsourcing, colour and detail. I hope some of this helps.
