Just to reiterate what steener said, make sure you let the engine run and heat up to a stable operating temperature before you start futzing with the needles. It's not such an issue on hot days, but particularly in colder temperatures, prematurely playing with the mixture can often lead to misleading behaviour as the engine often hasn't fully warmed up.

That said, take your time and follow Dauntae's excellent instructions and you won't go too far wrong.