You always want to adjust the idle when the engine is (reasonably) hot. When a well-adjusted engine is cold it tend to idle at a lower rpm and even die. You first might want to check the throttle servo. A medium to normal sized digital is preferred because it'll hold the idle position better and has a better resolution. Be sure the throttle won't open the full 100%, just below so vibration isn't transferred to it.

When the servo is fine adjust the needles as follows:
Run engine warm/hot w/o cowling;
Close the low speed needle 1/16 turn at a time and then accelerate the throttle fast up to the point the engine starts surging. Open the needle 1/8.
Adjust high speed needle for max rpm and cut it back 100-200 rpm by opening the needle a bit, about 1/16.
Repeat at least once. The LS and HS affect each other.

The low speed needle needs to be adjusted to a point where the engine in the lower rpms almost runs too lean. This will give you a smooth transition. If possible, disable the sub trim and use the radio's digital trim to set the idle. With a decent digital servo you'll never have to touch it again.

Edit:
Start above procedure w/ the needles set to the manufacturer's settings which will be quite rich. Your engine might already run too lean.