You should have an obvious idea of how your Statement of Purpose should represent you to the schools you apply for the admission committee before you start to work on a statement of intent. A quick checklist is given here:
10 Tips for Writing a Powerful Statement of Purpose (SOP)
Tips for Writing a Powerful Statement of Purpose- If we talk about studying from abroad, or one plans to go for the regress academic programs such as graduate programs and postgraduate programs, then one requires a fair amount of time and dedication in order to write SOP, since writing a perfect SOP will provides you with the guaranteed admission in the ivy league colleges who are numbered in the top listing of QS WORLD RANKINGS OF UNIVERSITIES AND COLLEGES.