The guns were done very nicely.
The smoke effect wasn't very fitting... it was obviously an added effect, whereas you kind of want to aim for making it as fitting as possible. When it comes to post-production effects you hardly ever notice that they're there in major films, even if the audience clearly knows on some level (like teleporting). I mean obviously there's a limit on what you can do at the moment, seeing as you've just started using AE, but when it comes to that "regeneration" effect the kind of look you should strive for is
this, whereas yours just seems a tad too... flat? I want to say flat, but that's probably not the right word.
The blood was also too misty. Blood is (basically) a liquid, not dust.
Overall though it's quite nice work, especially the gun fire. You also managed to accompany it with a not-terrible video, so bravo, aha

I'm sure someone else can help you a lot more than I can, I'm not much of an effects guy, but I like to give my two cents on the subject.