I usually re-roll this one as it is really not something you earn during normal gameplay but rather you have to really go for it and that is not easy and time consuming because you often do not have many opportunities. It is best to outflank lonely snipers or finish downed enemies that are close but that is not possible every time.
I also hate when you have impossible tasks like when I started and got X arty, mortar or flamethrower kills yet I was very far from unlocking them.
I also noticed there is great disproportion of difficulty/time needed to finish certain tasks. There are things like complete 1 game vs finish 1st 3 times or do 65 kills with SMG.
I see myself running like an idiot with a knife in my hand in Fortified Region, so I always skip this. As well as flamethrower and handgun. Instead I always do mortar, artillery and others.
Grab a bayonett and thats it. Its incredible easy to bayonet objectives if camping behind corners or flanking people who camp on windows and stab their backs.