I am getting lot of questions about PS. As per my knowledge and what I did Opening paragraph should be sensational and having some courisity so that the person reading it tends to read further.
1st paragraph why medicine should be something really interested.
2nd why your specialty
3rd about you rotations in medical school and volunteer experience.
4th should be on ur clinical experience in USA and y you wanna come USA.
5th why you are best fitted in the prog and what are you looking for in a program.
Write a rough sketch then approch your high school English teachers to make it grammatically correct and put some nice attractive words in it. After corrections ask everyone you know to read it. I mean your seniors your local area doctors. Everyone you know in US how they write n love to read in US. If you have some US attending known to you ask them to read you PS. Remove and modify if you think suggestion is good then it will be finalized in about 15days. This is what I did.
DONT TAKE PS LIGHTLY. DURING MY INTERVIEWS MANY OF THEM READ MY PS IN FRONT OF ME AND ASKED QUESTIONS.
Hope this helps.