Here are some tips for you;
1. Don't be afraid to get aggressive, timidness will only make the long climb to proficiency even steeper. Take your licks and learn from them.
2. Even if you think the other guy has you for sure, roll the 38 and always show the flat side (ie from the 3 or 9 o'clock), you'd be amazed how often people miss.
3. Stall limiter OFF.
4. Use the rudder to increase the roll rate of the P38.
5. Put convergence way out, not that convergence matters much in a p38, but it will throw the lead a little higher which means you can pull slightly less to score hits. Its a very small fraction, but advantages are always desired.
6. Don't be afraid of the flaps.
7. Learn how to cross control.