Origins BO2 Strat, (dont know if it works in BO3)

When you leave the first room, buy the door leading to Gen 3. Try your best to farm points asap to get the mauser PAP'd before the panzer comes, sometimes this isn't possible, but thats ok. Upgrade the ice staff and train until you reach round ~20. Camp in front of the first room Gen 2 door, which you didnt open.

Excellent camping spot, the zombies spawn fast enough such that you kill the zombies efficiently, and the panzer will always spawn right in front of you, so you can kill it in 2 seconds. If you get surrounded, just buy the door behind you and run. After round 50 or so, you can start training behind the tank station in the mud at Gen2, the zombies spawn pretty quickly at this point so they won't block you while training.