letter to work (not baby related sorry)

I need to write a letter to my employer to quit. I have secured work else where and want to leave but I am terrible at doing things like this gracefully. Does anyone have any tips? I keep postponing writing this, I really really dread doing this sort of thing. I sit down to write and draw a complete blank... should I mention my remaining holiday time, do I state the exact date of leaving how much of an explanation must I give for leaving, is there a polite way to do it. ekkkk.... I just want to put my head in the sand.