you are leaving, nothing else really is gonna matter, You can say, "Piece out Hommeys !" It really isnt gonna matter.
But you never wanna burn bridges even if the old job really sucked.
So I would simply say,
It regrets me to inform you that I am tendering my resignation effective "date" I appreciated the experience and knowledge I gained here but I feel this move is right for me.
Not sure of your situation you may wanna put why you are leaving. But in a good way.
You could add, "I have accepted another position which I feel offers me,
better quality of life,
chance to travel.
change to better career
more in line with career goals
or something else, doinng that may open the door for a counter offer. Sometimes you have to leave a company to get ahead in that company.