This will only be a quick one.

When playing solo you should always buy a quick revive first. Then keep your pistol and just knife zombies without shooting them. Once you have enough to get into the 2nd room and buy a gun go ahead and do it. This gun will keep you backed up instead of a buddy at early rounds. Once you have it save up enough to get to the power room and then once in the power room just turn it on and buy juggernaut slowly buy other perks and stuff. If you see randoms go for it iif in the first room immediatly head to the lobby.