I would like to know the basic principles and etiquette of writing a well structured code.
Many good points have been made above.  I definitely second all of the above.  I would also like to add that spelling and consistency in coding be something you practice (and also in real life).
I've worked with some offshore teams and though their English is pretty good, their spelling errors caused a lot of confusion.  So for instance, if you need to look for some function (e.g., getFeedsFromDatabase) and they spell database wrong or something else, that can be a big or small headache, depending on how many dependencies you have on that particular function.  The fact that it gets repeated over and over within the code will first off, drive you nuts, and second, make it difficult to parse.
Also, keep up with consistency in terms of naming variables and functions.  There are many protocols to go by but as long as you're consistent in what you do, others you work with will be able to better read your code and be thankful for it.
Good practices in writing MATLAB code?