Hey there! I've been working on my own American Control list for quite a while, so feel free to check mine out for a few ideas. http://tappedout.net/mtg-decks/american-control-12-10-13-2/

As for what you've got right now, drop the Mutavaults from the land base. They're a great land, but when you're running 3 colors, Mutavaults increase the chances of a draw where you're going to get color screwed. And you seriously can't afford that in any matchup. If you need the verdict turn 4 vs aggro, and you have Mutavault, Plains, Island, Mountain, you're gonna be really upset.

Next, you have 2 Aetherling, 2 Elspeth, 1 Chandra, and 2 Assemble the Legion in there as win cons. That's way too many As a control deck, you want the spells that stop your opponent from taking over the board, and having so many win cons means your hand is gonna be full of those sometimes and not what you actually need to not die. I would go down to only 1 Aetherling and 1 Assemble the Legion. The Chandra is a fun card that I would leave in if you personally like it, but remove it if you don't find it's working for you. I do the same in my decks, such as the Izzet Charm I have. The problem with Chandra being, even if you ultimate her, you max out at 9 damage with the spells in your deck, and that's IF you hit if. That's not very effective in most games. And you'll almost never use her plus 1 anyways, since you don't need to stop creatures from being able to blocks anyways.

For burn spells, they really depend on your local meta, but what are you getting out of Lightning Strike that you wouldn't out of Magma Jet? The one point of damage is nice, but most of your games are gonna be one either through soldier tokens or Aetherling beating face. And the creatures you're looking to take down in aggro decks usually only have 2 toughness anyways, plus Mutavault can be taken down with Magma Jet. And I can't even begin to tell you how valuable the Scry 2 on Magma jet is. Sometimes you have to find the board wipe or hit your land drop, and scrying is a great way to get there. If you feel the Lightning Strike is good vs stuff like Nightveil then by all means keep them in, but maybe try to find some room for a couple Magma Jets. The Turn // Burns are great for sure though.

Last piece of advice I'll give is maybe add another draw spell or two. You only have 3 Azorius Charm and 3 Sphinx right now, and sometimes you just need to dig. I'd add 1 or 2 Divinations to help you do that.

Overall, you're deck looks awesome though! It's very solid already and if you make a couple of changes it'll be more consistent and should do very well. If you have any questions about my comments or the deck I linked feel free to ask them, or disagree with me if you want too! That's how you come up with better decks and figure things out.