After reading this there is some tips I would like to add.
Medal of Commendation - 50
If you see someone knifing someone shoot them. If its a teamate you can steal the kill while they are doing the animation. Dual shotguns works well if you can get accustomed to it. I prefer a single shotty or Dual SMGS with silencers. If someones charging you with a knife jump around so they have a harder time hitting you.