I've been struggling with these critical missions for a while, I even asked a lot of questions in this reddit but didn't quite helped me. So I want to share here, the way I did it, as an Average Joe, I didn't get the improved results but with how I adapted, I'm sure I can do it.
In my run I had games with 8 critical hits and with 0 but in the end i managed to get 25 crits in 10 games so success! 😀
Step 1: I picked a tank: I had in garage almost all tanks from the Coalition tech trees so I started experimenting with each of them to see in which I get more crits. I decided that an autoloader medium would fit me the best and my two best tanks were Skoda T50 and Progetto 46. I decided to proceed with the Progetto for the games with tier 6 tanks.
Step 2: once i picked my tank, I have reseted my Gunner's skills and added Deadeye
Step 3: ammunition counted: i obtained at least 50% more critical hits while spamming Gold ammo and the fact that I picked a premium tank, it helped me to not lose significant amounts of credits.
Step 4: lights. i tried to shoot as much as possible towards lights, especially ELC EVEN, sometimes I got even 2 critical hits with one shot into ELCs
Step 5: of course, focus engines and fuel tanks to get fire. Here is one of the games in which I managed to get a good amount of critical hits
Good luck in the battlefield! 😀
Source: https://www.reddit.com/r/WorldofTanks/comments/x1jvi3/coalition_4_critical_hits_how_i_completed_it/