Historically, the best way to prepare for the next war is to be as ready as you can for just about everything. This means well trained troops, carefully selected leaders, and a lot of equipment you think you wont need. Most of the time youll be wrong, but will end up better prepared than your opponent.
Over the last few decades, the American armed forces also developed an extremely powerful weapon, without really trying to. This we can call the reality weapon. Wars always open with everyone using unrealistic, unworkable and often fatal ideas developed through long years of peace. Call that reality drift. The longer an army trains during peacetime conditions, the more doctrine drifts from the reality of combat. It's an ancient problem, that has been solved somewhat by NTC (the U.S. Army National Training Center). The aviators found similar wake-up calls in their Top Gun and Red Flag training programs. The navy has had a similar epiphany when they trained with Australian and Norwegian diesel-electric subs recently. The navy found that diesel-electric subs, manned by good crews, could do enormous damage to a carrier task force.
Unexpectedly, a major source of "combat experience" was obtained from the NTC training sessions. It took a few years before anyone realized this. But when data from NTC exercises didn't match the "theories", but did conform to "obsolete" World War II, experience, it was obvious that something was happening. But not everyone was convinced. As the old saying goes, "It may work in practice, but does it work in theory?
But now there is Afghanistan and Iraq, which are providing practical experience that is again closer to what went on at NTC, than to theories that were being dreamed up by staff officers and pundits. So just keep in mind that reality is a slippery beast. Expect to have a hard time holding on to it. There were always be more attractive, and quite false, alternatives presented to you when theres not a war going on.
American military planners are trying to get ready for the next war, and they are sorely tempted to reorganize everything to refight the wars we are currently involved in. Some people never learn.