Here is my guide on effective ways to farm the components needed to the infernal machine, as well as some strategies for the uber battles that I have observed during my time with the game.
This is probably the most annoying part of process, so lets get it out of the way. The plans for the infernal machine are dropped by the keywarden in Act 4. The annoying part of this, is it is very hard to get a full five valor stack before reaching the area where the keywarden is located, which adds ontop of the frustration that the enemies normally give you in this act. So, on average, you can pick up four elite packs between the two garden areas, if you are lucky, you get the full five, if you are unlucky, you only get three. From my time farming, I was happy if I got four, and I usually found at least one elite before running into the keywarden. If I found the keywarden before getting a fifth elite, I would try to lead him away from the checkpoint and just die, and made sure I went a different direction when I respawned to find another set. I personally farmed this on a lower MP levels, just because at higher MP levels, the mobs get really frustrating if you are not geared to survive it. It took me about 20 runs at MP1 to get it, but it was not as frustrating as trying to get it on higher MP levels since I would rarely die at MP1, so I was able to get more runs per hour with less headaches.
If you've endured the process to farm plans, then this is relatively easier. Lets break it down by each act. These are my choices based on running at higher MP levels with my CM wizard versus my Demon Hunter. So the route choices are more focused on elite killings versus while dealing with the least amount of mobs. Although the Act 2 keywarden is ridiculously easy with a Demon Hunter.
Act 1. Get your valor buffs in festering woods. Usually you can get 3-5, and then hit up leorics manor to get the extra stack if you don't get 5. Even if I had just 4, you can easily get the last stack while searching for the keywarden. But if you want to play it safe, you can hit up the Cemetery to top up.
Act 2. There are various ways to get your 5 valor stacks. My old method required you to find the Cave of the Betrayer and using that checkpoint to do a series of runs. You can usually pick up 4-5 elites in this cave, but finding it can be annoying, so here is the new route; Black Canyon Mines for 1-3 stacks (sometimes more), and then Road to Alcarnus for the extra one there, then I get my 5 stack while looking for the Key warden in the Oasis.
Act 3. There are couple ways to get the 5 stacks for this area, a lot of people like running the keeps because its close by, some like doing the first two parts of the Alkaizer run. I like to goto the Bridge waypoint and look for the Cave. I like the cave because its low mob density, and there's a guaranteed resplendent chest inside for a free stack. If I was playing lower monster power levels, I'd probably stick with the Keeps 3 & 2 to get the 5 valor stacks, or using skycrown for the stacks.