zx 5 rtr, what to upgrade???

[mary_p_o_o]

i have just purchased a zx 5 rtr and am intending to race at my local track, i am a newbie to rc racing and in need of some advice,
as i am probably going to stuff it sooner or later ( probably sooner) i would like to be prepaired, which parts of the rtr would you guys recommend to upgrade for strength and/or performance???
cheers guys, mike