Your introduction and even your first sentence are the most important part of your personal statement. This is where you can grab the attention of the admissions representative. Make your first sentence unique and compelling. It is recommended that you state in a creative way WHY you want to undertake this field of study in your first sentence. The rest of your introduction should provide a brief explanation that supports this first statement. Divide the word limit by the three parts of your personal statement by allocating your introduction around 30%.
Remember, your personal statement is 'personal' in nature so it is in your best interest to be sure that all the information you provide is in fact your information. By starting with one sample and taking some ideas, then moving on to another and taking additional ideas, and so on, you allow your true self to come out in the finished product and this will give you the best shot at gaining access to the school of your choice.