Don't feel bad about losing your first PBEM game... that happens to everyone in this game. I lost my first one terribly too, and I thought I was prepared going into it. I also lost badly in my second and third attempt, though by the third I was doing much better. This is a fairly complex game, and certain aspects are tough to learn (or even understand) without seeing the bad side effects that happen when they aren't done right.
IMO, the very first thing to do is read this Wiki page
AACW Wiki Overview
It is jam pack full of some very good info that is core to understanding and doing well in this game.
Secondly, read through old posts here on the boards, there's a lot of good stuff out there, especially considering this game is 5 years old now.
Lastly, ask questions on the boards, the folks over here are very helpful and can give good insight. Put as much info up in this AAR as you can, I'm sure you'll get some good feedback.
Keep in mind there are 2 really important dates. The first is October 61, when divisions come available. You need to be ready to start building them as soon as that date comes around. The second is March 62, when Corps become available... again, you want to get these going ASAP. Both greatly increase your forces' power, both on attack and defense. This area of the game is tough to fully grasp without going through it a few times, if you have time available, you should try playing the AI up through those dates to figure out the mechanics.
Watch your units health and cohesion closely. When possible, you want these high, preferrably 100%. Attacking with units that have low health and/or low cohesion is asking for disaster, even if you have good odds. When cohesion gets too low, you start risking routs, which are really, really bad and can drag the rest of the force down with it. At 100% cohesion, even losing a battle badly usually doesn't result in a complete loss of cohesion, but at lower levels of cohesion, you are playing with fire.
As a rule of thumb, aim for odds of 3:1 or better for attack. Otherwise, you aren't likely to win.
Also, I've come to believe that defenders should *ALWAYS* be on Hold At All Cost. Otherwise they tend to just run away if the attacker brings even a marginally substantial number of troops. Hold At All Costs means the defenders will hang around for at least a little while, and usually they still retreat before getting completely demolished. Any way going it's easier to inflict heavy casualties on your opponent when you are the defender as opposed to having to counter-attack.
