Generally I write a 1-2 paragraph thing that goes:
Dear Editor,
We are excited to submit this manuscript regarding blah blah. As you know blah blah is a condition/topic of significance because of this reason and that reason. In this study/review we did this and this, and found that and that. Uniquely, this finding was of particular import. These results are of much interest to so and so as well as such and such. We hope that you will consider this manuscript carefully for publication.
Regards,
signed corresponding author
