i'm sorry but I find these things/places to be a waste of time. Just write about yourself, if you are applying to LS you should at least be able to convey who you are and your ideas in a decent manner. Get a friend or someone who is good at grammar to edit for grammar, have others edit for content.
Another that works is reading other good and bad PS, see how the goods succeeded and how the bads failed--mainly it is about been honest and finding a bomb ass topic