Go on support, pick your favourite LMG (I used an MG4), select ammo box and claymore. Always go to the Firestorm tower (not Caspian, because everybody always tries to blow it up).
Start Conquest on Firestorm (and maybe hope you're on RU), head to the tower by C, climb up the first ladder and just stay there. Put a claymore by the ladder, everytime someone climbs up they'll be killed (which will count towards the assigment), then keep on replacing it every time.
The opposite team will start attacking the tower and C/E, so you'll be able to rack up a few kills in no time with an LMG. Just be mindful of people trying to snipe at you from a distance (probably with their GOL Magnums).
After that's done, all you need is the sniper rifle ribbon, all I did was equip the Scout Elite with a 6x scope and hang around where there's plenty of infantry. Sure you'll get killed but with the 6x scope it's quite easy to get a few kills and then you'll get the ribbon.
Good luck.