Hello - yes this is a tough subject. I have written a few advice blogs on how to write a synopsis and preliminary letter on writing site Write & Share. To read my article and view my synopsis for my novel please click this link:
After sending my letter, synopsis and first 3 chapters of my book to an agent, I got a reply from the editor requesting to read the whole book. I hope that they like it and decide to take me on. The point is that my work made it through the slush pile and to the editor which I'm happy about. I hope my article helps you.