One thing i have noticed about the ranks is i rank up the fastest when i go through levels in the game the fastest(not leaving a crawler or something) and if you hit the box and shoot a lot of bullets you rank up, but you rank up the most for being an all around player when you play as well as getting far with little to no downs.

Because your k/d is only a 72 has to be a 90 to be skull

I had the same problem, so I experimented a little and found a way to rank up quickly. I started a new character and earned the knife in one week and the shotguns in two. I played custom game, on EASY, of survival in the town. Yes, playing on easy does contribute to rank. Just make sure you're playing "online". The town has everything you need, including a mystery box and a pack-a-punch. Finally, I did a lot if quitting. You can quit at any time without it counting as a death. I received the shotguns with 19000K/25D and a .9 accuracy. That's my story. Hope it helps.

Play tranzit it makes you rank up faster but u have to get little downs and alot of kills. Right now i have the 2 shotguns