Question regarding negotiations in leasing a car.?

i have a 2010 sentra base and am going to trade it in next month and terminate my lease early( Nissan allows for this with no penalties as long as your payments have been on time for 12 consecutive payments) and i am going to trade up to the ser spec v edition Sentra. i'm still pretty new to negotiating and stuff so whats the best way to negotiate to get the lowest possible lease payments and also get good interest rates(well if interest applies during leasing.) now when i get this car i plan on buying it after the lease is as long as everything goes smooth. Nissan comes with a 15k year limit but you can opt for 18k with a higher price. what are some things i need to look out for and things i need to press hard on to get the best possible payments. i go to mossy Nissan in Texas and my sales oc is the top rated at the dealer and was the one that leased me my 2010.