At the end of the day "Smack Town" is easily one of the hardest missions on special ops to 3 star. I found this mission much easier to do in solo (which is very strange) i completed it the other day in under 3 trys (solo) after trying to complete it the night before with one of my mates (took us way over 20 trys).
Make sure you stay using the light machine gun thoughout at least the chopper part, i really wouldn't recommend the assault rifle, you get too many hit markers and have to reload all the time but dont get me wrong the noob tube (grenade launcher) can be very useful at times, use it at your own risk..
Now i find the chopper part to be the hardest part of this mission. Basically all you want to do is pick your targets and fire short controlled bursts, this makes your bullets much more accurate and guarantees a longer period of time before you have to reload. I know sometimes in the video i went mad and started spraying at a couple of guys and it took me ages to kill them thus why you use short controlled bursts, i was just panicking at the time (thats my excuse) ;)
I recommend reloading your light machine gun when you see a good opportunity e.g. when you clear the current wave of enemies and there are only a couple left. Reloading at the wrong times on this chopper can really mess you up (i know this from personal experience).
Just before your choppers about to touch down make sure you blow up the jeep in the distance. As soon as you drop from the chopper take cover behind the barrels in front of you and camp there until you have picked off all the enemies. As soon as you drop i recommend shooting the people on the left 1st because occasionally the RPG guy shoots a big ass rocket at you and believe me you dont want to fail just because of that biscuit.. once you've dispatched the first of the bad guys, make your way up the right side of the map and enter that building. take your time though, there are quite a few enemies that hide round the corners. Make your way up to the top floor (the roof) and straight away go prone. Take out the enemies on the opposite roofs and plant the 1st bomb.
Once you plant that 1st bomb drop down round the back side and take out the enemies that appear when you drop down. Now slowly make your way to the next building, i recommend following my video for here on out. just make sure when you plant the second bomb, camp inside that building and pick off the enemies that appear, when you think they are all dead, exit from the far right side of the building, blow up the C4 and "get to the choppa!" Anyway good luck and i hope i helped you out =]
Note* Sometimes the sound in the video goes all freaky leaky, i have no idea why but shit happens i guess.. Also due to my videos being uploaded in widescreen they dont seem to fit in the small video box on trueachievements therefore i would suggest you turn pop ups off and click on the text in the video box to open up a new window where you can view the whole picture.