The personal statement is also a great place to explain more serious problems, like less_than_ideal grades or test scores. Don't be afraid to write something like, "I don't test well" in the statement. As long as you can provide a good reason for you app's problems, it's okay to address them directly. You won't be able to hide it from admissions officers anyway, so providing a reason for problems is always preferable to ignoring them.
Having known about the importance of personal statement, the next question emerging in our mind is that how to write it? Take a blank piece of paper and brainstorm a list of your skills, work experience, personal interests and qualities which are relevant to your application. Jot down these issues before you carve sentences and paragraphs. Be personal and concrete. Tell issues which makes your application unique from others. Be enthusiastic and show what you have actually done, and why you found them interesting. It may be very difficult for the academic officers to select you if your personal statement is not up to scratch, particularly when there are thousands of other candidates to choose from. You can qualify for the desired university only by writing a perfect personal statement; otherwise you may miss a chance, though you are academically sound.