I would recommend:
1.) Play some of the folks on this site via forum (using AABattlemap) or live via Triple A. Playing a variety of players, and gaining exposure to someone else’s play habits besides your brother and your own, may give you ideas on what you should be doing. If you can snag somebody decent (who will clean your clock) then you will learn a lot (by losing). You can then apply those lessons to your game with your brother.
2.) Read the submit articles section of the forum for openings and general strategies for each of the five powers. There are some good articles to be found there. Even ones written for Revised will still apply for Spring 1942.
3.) When your brother leaves the room, swap out several of your grey chips under infantry stacks for red ones, then add a few grey chips under the fighters and aircraft carriers. Just be sure to add these chips to your side and not his. Also, if playing Russia, add a Battleship or two to SZ 16 - he will probably not notice this as Russian BB’s are common purchases and he may have lost track of how many you have done. Afterwards, do not leave the room yourself or the same thing may happen to you.