How to avoid confusion about whether a deal is official
Do tell the other side in writing that there's no deal until you sign on the dotted line.
Do repeat the above step in every piece of written correspondence.
Do place a disclaimer on every document you circulate that reads: "Draft-for discussion purposes only-not intended to be a legally binding document."
Do insert contingencies, conditions, approvals, etc. into your negotiations.
Do refer to "proposed" deals using the future tense and the conditional mood: "The agreement we might enter into would .. "
Don't make any statement inconsistent with the above.
Don't agree to any important point without specifically making it contingent on every other point in your agreement, whether major or minor.
Don't throw big parties, make announcements or take any public action that would make others think you've struck a deal.
Don't perform your side of the bargain.
Don't let the other side perform their side of the bargain; let them know in writing that they do so at their own risk.