How do I get recommendation letters?
Given the OP’s situation explained in his question and the following comments that he has trouble with getting recommendation letters written by his professors themselves, if I were him I would


  
    Find the professor who would write the recommendation letter himself.
    
    Find the professor who taught the class which I had very good grade.
    
    Find the professor who taught the class in which I was most interested.
  


Usually, I need three recommendation letters. Now, I have three.

My personal experience is that I tend to have good grades when taking the class I am very interested. If I had good grade in a class I was interested, the chances are the professor would remember me and more willing to write the recommendation letter himself for me.