Death By An Arrow Makes the Art Happen

In terms of drawing humans, I highly suggest learning how to draw anatomy first. And not just proportion ratios, but also skeletal structure/function and how muscles overly that structure. This is probably one of the most important foundations you'll need if you want to start drawing figures from non-references.

Find books to research on and do lots of studying. Also draw a lot from life whenever you get the chance. I have a good anatomy book somewhere in my closet that I'll dig up later on.

As for clothing and armor designs, it comes down to one thing. References. Lots and lots of references. Try to decide what style, era or genre of clothing/armor you're going for, and just do a ton of research related to your subject matter. References are a huge asset for artists. It's very rare that artists can make up successful costume designs completely off the top of their head with absolutely no prior reference or practice.

It's better to have reference on hand rather than assume you already know how something looks and draw blindly. Practice a genre enough, and you can get to a point where you can actually free-hand the subject matter.

As for personality, that comes later. Being able to express proper emotion or personality comes a lot through gesture or posing of a character. For my Character Design class, this is a lot easier since we're working more in an animated style and therefore don't have to follow the rules of anatomy. However, for realistic figure drawing, you'll have to have an intermediate understanding of anatomy since it's the exact opposite of breaking down characters into exaggerated shapes and forms to express their traits. This, 100%. Reference and understanding of the form are everything.

Actually, just yesterday in my Drawing class my teacher commented on how my sighting was so good when I draw people despite how much I struggle with sighting objects. I chalk it up to having taken Human Anatomy and Physiology in high school (understanding skeletons and muscles = really really helpful) and that my art teacher in high school forced us right off the bat to learn the canon of the human head. Knowing how everything in the body goes together makes everything much easier to understand. You get to the point where, if something is off, you'll notice it, because it will just look wrong.

Aside from learning all that, try doing some gesture drawings. They're great for learning how the body moves and bends, and then you have a handy base if you ever want to draw someone in that position. Note that you should only be spending maybe 30 seconds to a minute on these. It's a good thing to do to amuse yourself while you're bored (I used to do them all the time in my Islamic Civ class), and it'll be useful too. Gesture drawings are also a good way to start an image - just spend a minute or two working out the overall shape of the pose, and then flesh it over. I always start with a gesture.

And references are amazing. Start a collection. I made my parents lug my entire collection of National Geographic magazines halfway across the country so I could have them here at college, because they're full of great references for pretty much everything (those DK Eyewitness books are great too, especially the ones on animals where they show the skeletons). I also remember being struck when I read John Howe's book Forging Dragons, in which he talks about his references - he keeps entire files of "lizards" or "trees" or "gargoyles". References are your best friend.

If you can't find a reference of a pose, of course, just get someone to do it for you. My suitemates have gotten used to my asking them to model for them (I also keep several pieces of PVC pipe of varying lengths around for them to use as props when I'm doing a fantasy picture). Try curling your hand into the shape of the one you're drawing, seeing how the muscles move.

Oh, and even though references are your best buddy and you should use them all the time, try to draw from life whenever possible. At the very least, do some surreptitious sketches of people (a friend reading or working, somebody a few tables over in a restaurant, the person next to you in a lecture class) so you get a feel for the three-dimensionality of the body. And always always always try to draw portraits from life only. Photos tend to flatten out the features and distort things in odd ways.