Lag is a recurring problem that seems to come and go, disappear and get worse depending on the latest patch. When you have to put a mag into someone to kill them that is usually the result of players from abroad playing on domestic servers and there is unfortunately nothing that we as a community can do about that on console - on PC they have region and ping blockers that help but doesn't totally solve this problem. Foreign players on domestic servers also cause the magic bullet effect where bullets follow you around corners to kill you which is very frustating.
There are fortunately a couple of things that you can do to help to mitigate or prevent lagging or freezing on your Xbox but it won't address out of region players. One thing is to ensure that you have a good amount of HDD space left since computers don't run efficiently when the HDD is almost full. BF3 plus Premium with all expansion takes up around 20 GB.
You can also plug your console directly into your router with a Cat5 cable instead of using wireless to play online games, you can install the game to your hard drive (this creates a faster read and reduces heat since the console isn't spinning the disc) instead of having the console continuously reading the disc, ensure that your Xbox is clean and located in a clean well ventilated area since an overheating console will have lagging and performance issues, and you can clear the cache on your Xbox. I've experienced lagging with Skyrim and Dragon Age II and the issues went away when I installed the games to the HDD and cleared my cache on a semi frequent basis on my Xbox.
How Clear Xbox cache:
To clear your Xbox cache. (it won't affect your single player or multiplayer games)
To do this, go to your XBox dashboard,
Go to settings>System>Storage
Go down to "Hard Drive" and hit "Y" for device options
Go "Clear System Cache"
Other than what I've just written there is little that you as a player can do to address lag issues.