I have to do this for a living, so without wishing to get in to an argument about my advice, take it or leave it, without sounding harsh it makes no odds to me.
1, keep it friendly.
2, do not keep putting your finger on that chip you just found, its a used car, if you want a car without a single stone chip then buy a new one.
3, try & keep the conversation going, don't try & play hardball, it works both ways.
4, please please please do not try & squeeze the hell out of the deal, asking for fuel/mats/flaps or any other thing still costs the dealer money, its the same as taking money off the car unless you can ask them to swap stuff like wheels/tyres or mats from another car they have in stock as that is doable, probably.
5, go in as near to the end of the month as possible, if they haven't hit their targets you could get lucky, but if they have your stuffed.
6,7,8 & 9, have I mentioned keep it freindly, even if it doesn't work out there maybe another car at the same dealer so don't burn your bridges.