Here are a couple of tips to help you get on your way.
Since you are already an excellent P-51 driver, flying the P-38 should be an easy transition. Until you get used to using the flaps in turn fighting situations, fly the Lightning like you'd fly the P-51.
Do not use Combat Trim in the P-38. It hinders you more than helps you and can keep you from flying the P-38 on the edge. The only trim you need to adjust (unless you have battle damage to the wings) is the elevator trim and even that you don't really have to touch. Just set your elevator trim to the horizontal bottom part of the L on the elevator trim indicator.
If you don't mind reading some or watching some films, here are some links to various threads and films on the P-38.
Here's a link to a crap load of P-38 films.
P-38 films Here's another link to some P-38 films that Leviathn had made for me to help me transition to the AH P-38 after flying the AW P-38J for so long. One of the films is an excellent training aid on how to use flaps as he shows how to endlessly loop a P-38 by just using the flaps to generate the necessary lift.
Leviathn's P-38 films Here are some links to different threads on the P-38 where some of the other excellent P-38 pilots in AH discuss some various tactics.
A hand with the P-38 A question on verticals P-38 driving questionsHere's another link to a film of me in a P-38 against a 205. It's a long film, close to 10 minutes in length.
P-38 vs. 205Here's a film of a duel with a Spitfire Mk XIV.
P-38 vs. Spitfire Mk XIVAnother film where I get into a fight with a 205.
P-38 runNext time your in the MA, check the roster to see if I'm online and I'll be more than happy to go with you to the DA for some sparring. You can also ask guys like Murdr and BURNM (both excellent P-38 drivers as well) for help and tips.
Ack-Ack