For me, a combination of endurance and strength training works. However, everyone adapts to altitude differently. I can not over emphasize the need for proper accimatization, especially since you do not have any prior experience to draw on. Once accimatized, you will probably find you have the same strengths and weaknesses at altitude as you do at lower elevations.
The need for endurance is obvious; however, at altitude, heavy packs just kick my ass. Therefore, I spend a lot of time training with heavy loads. Above 15k every pound feels like 2 and about 20k every pound feels like 4 pounds.
But heck, you might be one of those super-humans that perform exceptionally well at altitude. Me, I'm the essense of average and rely on training and desire to get me up the big peaks.
Good luck - the Great Ranges of the world are incredible places!