Okay, I pretty sure you don't have a clue by what I mean when I say the "basic stance" so let me explain. It's the pose you will find the Guyvers in more than an other single stance. Every guyver has been drawn standing this way at one time or another and knowing how this stance is drawn lays a good foundation for doing other stuff with the Guyver.
Now for a visual explanation, This:

Is a good example of the guyver stance.

Now outside of the very basic stance you can modify it to give the drawing a different feel. As a rule of thumb modifications to this stance generally involve changing the position of the arms, crossing them or placing on hand on a hip are good examples. The other thing that's allowed is to change the direction the Guyver is looking.

In example making him look downward and bringing his near arm up to show off a clenched fist will make him look angry or defensive depending on if it's GuyverI or GuyverIII(or possibly GuyverII or an original guyver) In the same way crossing the arms over the chest will make a Guyver seem either defensive or imposing or in some cases a little of both.
Although it's most commonly used when drawing female guyvers placing a hand on a hip will usually portray cockiness and tilting the head in addition will make it seem as though the drawing is trying to taught the viewer. Now of course there are a lot of other things you can do to modify the basic stance and all of them will achieve slightly different results. The big point I'm trying to make is that most Guyver art is just a modified sense of this pose.

Although you start to stray from it when you move the legs around in the end most positions are still relatable to this stance. If you wanted to draw a guyver firing a pressure cannon you might spread the legs a bit and arch the back, the arms would come forward in front of the waist or to one side depending on the look you wanted. The hardest thing about moving that far from this stance is that you then have to start worrying about balance, (which I'm not going to do more than mention here since that's something that'll be going into another tutorial) since it's easy to draw the figure in a way that it'll look like it's falling over backwards or something.

Coming back to the main point. The basic stance can be broken up like so:
This can be done a lot better free hand by the way, but you can see the shapes that are used pretty well in this example and it's what I've got on-hand right now so he'll do just as well. Now you don't have to put this together in any order but here's how I usually assemble this guy:
First off I draw in a sort of line of balance, usually more or less where the spine runs through (shown in blue). This is what everything else is built on. Off of the spine I draw a loose skeleton (It's really just a stick figure, shown in green). You might want to note that this isn't the same sort of stick figure you would use for drawing, say a normal person. It's especially evident in the legs where to an extent the legs seem to arch backwards. No that's not a mistake.

In a great deal of comic/manga/anime type artwork certain aspects of the characters tend to be exagerated (this is especialy true of 'superheroes' and any type of armored persons), in this case the calves tend to arch sharper than they would in real life. Now if you really want to you can force these guys onto 'normal' human frames but as far as I'm concerned it's a pain in the butt and I'd rather actually get the rest of the drawng done than spend any more time than I already do messing around with the pose.

Back to business, both when you're messing with the stick figure and during later steps try and keep the Guyver's proportions in mind. Like many manga style characters a guyver's legs make up the bulk of the height on these guys. If you look the length of the thigh is equal or close to it to both the length of the calf and the length of the torso so for the most part you can divide this guy into three equal parts and a head. The arms should reach to the thinnest part of the waist, or just above it, at the elbow, and the lower arm and upper arm should be more or less equal in length (be sure and measure from about halfway into the shoulder or about where the joint would be).

Once you've got the proportions and the stick guy and all that done the next step is to flesh the guy out, I usually go about doing the lower torso and legs first since whether or not this guy looks like he can stand up depends a lot on them. I outline the shoulders next and sort of fill in the chest and waist loosely after that. I almost always do the arms and hands next and the head last, although on occasion I switch those two around. It doesn't really matter what section you do first so my recommendation is to try it a few times and start with whatever section you're best or most comfortable with, that generally sets you up for a good overall sketch.

By this point you've got something that looks (more or less) like the guy above. Usually at this point I get a new sheet of paper and trace over just the outlines and maybe a few guide lines, like where the joints come together or something, wherever I feel like I'll need them. If you don't feel like tracing you can just go through and erase a lot of the extra lines, as you go having them around can get more and more confusing, just be careful you don't erase anything important by mistake.

And now on to the fun part... (Personally I think this is the easy stuff, the hardest thing is getting the proportions and pose to look right. I have to try three or four times sometimes to get something I'm happy with.)
Now this is a drawing I did of Guyver3 recently so I'll use him to show what I'm talking about.

Once again when I'm drawing I usually start with the legs, the armor should lay just slightly outside of the outline while the organism (which hasn't been drawn in here) underneath should lay directly on the outline or, if necessary, slightly inside of it. Make sure and leave a small space at the back of the knee.

Also, even though it doesn't look like it at first the inner joint of the thigh (where the armor wraps around and joins on the inside) comes together about mid-thigh or just below it.

The top of the leg armor will NEVER extend all the way to the narrow part of the waist but rests more on the hips. The visual orb will lie more or less over the stomach or if you draw a guide line for it, it does rest on the narrowest part of the waist.

The swords generally rest on the elbows but keep in mind that the base can extend from 1/3 to 1/2 of the way down the forearm. Where the the upper arm meets the shoulder the organism tends to bunch up and out a little rather than lying flat on the frame.

I wish I could go more in depth in this part but the truth is the best way to figure all this stuff out is to play around with it and try and visualize or guess where a lot of this stuff should fit and see if it works that way drawn in.

I usually wait to add the details of the organism (all that stuff under the armor) until I start coloring these guys but if you want there's no reason you can't go ahead and do that here, and if you're not planning to add any color them Viola! you're done (although color or not I'd recommend adding some shading or something, it makes things so much more finished looking, but like I said that's up to you).

A few last notes on this stuff:
This pose is IMHO probably the easiest way to get used to drawing guyvers. The best advice I can give you is to play around with it until you start to get a feel for all the little parts, it can take several tries to really get it all worked out but once you've got it..
This is also a good way to start out characters sketches for original Guyvers. It gives you a nice overall view of what you're trying to get across.
And last but not least.. you gotta start somewhere and it might as well be here.

And thus we come to the end of this tutorial (my first BTW) as always I'd love to hear feedback, if you have your own suggestions to add or even if you think I'm full of it.

On another note, I'm looking for suggestions on some other tutorials to add here, so if there's something you want to know how to draw (and I actually know how to draw it) let me know. I can't promise I'll be able to put to gether a tutorial (or if I can if it'll be out anytime soon) but if there's something that a lot of people are interested in I'll see what I can do.