Statement of Purpose most commonly known as SoP is nothing but an academic essay which you need to write in order to state the reasons as to why you want to be a part of the particular grad school, where you wish to pursue your higher studies at.
Different universities may appear as if they are asking for different things. But, in reality all these universities want to know the following:
* Why/ what is the reason for you to choose that particular university to study?
* What do you aim to study?
* What is your experience in the relevant field?
* What will you be doing with the degree you will be awarded with?
You must be clear about why and what you chose to study. Your concerns about the subject and your interests about researching and developing the subject must be mentioned. It should show that you are thoroughly committed to the subject and you are a conscientious student.
Do not go off-track:
Many end up writing paragraphs about their skills as a dancer, writer or a singer etc. However, these things are not what the admission committee is looking for. You can mention your achievements in extra-curricular activities, but emphasis must be laid on how good you are when it comes to committing yourself to a research work or subject related work. Can you teach undergraduate students about a subject which might have a great future for all? What will be your caliber in grad studies? If there are activities which includes these, then do mention them. Like paper presentations, seminars, scholarships, awards won etc, pertaining to the field of interest.
You can discuss briefly about an idea. Make sure it is relevant to the field or course you wish to study.
Provide enough reasons why you wish to pursue higher studies in that particular field you have applied for. Make sure your reasons are realistic and approachable.
Do not repeat things:
Do not re-phrase the same sentence in 'n' different ways throughout the SoP. You need not write a literature like essay. It has to be readable and your ideas and interests must be put across without ambiguities.
Never get desperate:
Do not show your desperation in SoP to get into the university. This includes praising the university and the faculty.
Share and show the Statement of Purpose to the professors and friends. Ask them if they were able to get your point in the right manner. Get someone to proofread your essay. Make sure there is no grammatical errors and spelling mistakes.
Keep in mind that you are showcasing what you have, trust your caliber and put your words across and you shall be through.