Subject + decide + not + to + verb
By applying the aforementioned formula, the sentence should be, "You decide not to say anything ..."
Where possible, according to English traditional grammar, keep the 'to' next to the 'verb' to avoid split infinitive.
Reference:“I Decided Not to Continue/I Decided to Not to Continue.” Word Reference. vBulletin Solutions, Inc. 18 Feb. 2007. Web. 31 Mar. 2013.
“To Decide Not to Do or Have Something.” Macmillan Dictionary. Macmillan Publishers Limited. n.d. Web. 31 Mar. 2013.
“Deciding Not to Decide Gay Marriage.” New York Times, the. Arthur Ochs Sulzberger, Jr. 25 Mar. 2013. Web. 31 Mar. 2013.