The 3 points you want to get across can be accomplished in just a couple of sentences that include (a) your announcement that you are quitting, (b) as of a certain date, and (c) provide information about your last day.
State Your Intent. The whole theme of your resignation letter is the statement that, well, you resign. You don't need to play coy__the time has passed for you to fish around for a counteroffer if it's gotten this far. At this point, you've made your decision to leave, and this letter needs to reflect that.