WHOA, model making really isn't kid's stuff now that I've tried my hands on it.
I decided to make a simple model out of curiosity approximately some 11 days ago and started reading up stuff. Being a total stranger to model making, I found out that newbies like me have to quickly learn these:
1. A model-making tool. (In my case, Milkshape.)
2. Learning about creating textures, UV mapping, and using their respective tools. (In my case, I had to learn using GIMP.)
3. Learn about all the associated file extensions, how to use, and how to convert to the appropriate type while exporting your models. (Must be able to use MDX<=>MDL Converter, BLP Converter, etc.)
4. Learn to use Magos Model Editor to finalise your model.
5. And finally, research, research and read up the tutorials written by the experienced model-makers!
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So, for those who have decided to try making their first model, just remember that- patience, a willingness to learn various new tools, and a never-give-up attitude is that key! Because after trying your hand at model making you would most probably have renewed respect for our existing model makers.
Anyway, I have a minor things to point out the mistakes that beginners like me could make. Most people aim to make a humanoid model at their first try. Unfortunately, I think it is also very tricky to make. Apart from giving your model an acceptable outline, certain problems will occur during animation that wasn't obvious to us while we create the mesh.
Special attention should be put at making a smooth 'joint area'. Examples of a joint are knees, elbows, or the arm of a crane. Below is a pic of a knee that I made. Everything looks fine on the left picture, while I was shaping up a leg mesh. But the picture on the right shows the problem once I animate the model. The bending of the knee lacks a smoothness to it.
The way to correct these ugliness is shown below. Instead of having one single line of vertexes at the joints area, I now make two lines of vertexes, which are joined in a 'V' shape at the tail end. Then assign the knee bone to the lower line of vertexes, while the upper line of vertexes should be assigned to the bone directly on top of the knee. So when I now animate the knee, it looks much smoother
Also, beginners should always save often, and under different file names. I tend to keep making mistakes during animation and find myself rolling back to the previous good save.
And finally, my cheapskate model after many sweaty nights :'(

(notice the jerky knee-joints)
So even if we are disheartened by the result of our first model, we should always remember the time-tested mantra of "Practice makes perfect". First tries always tend to be error-prone. Don't give up and good luck modelling! (As for me, I found out that model-making is not my cup of tea ;P Gonna stick with something else.)