Steam Problems: If achievements aren't unlocking, you're probably on a Mac. In order to get Steam achievements to unlock, you need to take your save, put it on a PC, open the game with your Steam account on that PC, and when you load your game, all your achievements will unlock.

Achievement Problems: Some of them not working at all? The reason is that you need to get certain grindy ones WITHOUT DYING. This means you have to shoot 20k bullets, in one game, without dying (other are the four turrents, kill so many zombies, play for an hour, etc.). Because you can't technically quit the game without suiciding, this also means you can't quit the game. You have to do these ones in one shot.

Leveling Up: Hate to say this, but you need the highest level (13) in order to do well. You will likely just be playing for the sake of leveling until you get this.

Making Money: Scrap metal is money. The more ground you cover, the more money you get. Staying in your base at night is safer, but you won't make that much money. Whenever you see a chest, shot it open. Whenever you see a big metal (tank, etc.), break it apart.

Running: Double tap left/right to jump, and hold it while jumping. This makes you move faster. Do this ALL THE TIME. You basically move as fast as the most expensive boots, without buying them. This means more scrap metal because you cover more ground.

This is super quick, not in depth at all.
Once you have a decent level (at least golden AK47), you can survive every night outside, moving as fast as you can, in order to collect as much scrap metal as possible. Just plow through as fast as you can. Getting to the end of the far left or the far right is pointless. Just go through a whole level (corn or snow) and zone to the next level, then just immediately zone back to that one (corn or snow) and go through the whole thing, and zone then zone, do it again. Stock up on lots of ammo so the only reason to go to base is to upgrade.

You want to upgrade your characters, NOT your base (at least at first). First upgrade is the AK47, then go for armor or the other max weapons (when you get the Russian and German). Do NOT buy the other guns, only the best ones (this saves money). Don't bother upgrading boots until much later, because the running trick makes you move that fast anyways. Always keep numerous medipacks on you. Once you have the three best weapons, armor fully upgraded, and like 4 medipacks, you should be able to last outside all night, until about night 13 or 14ish. If you do this right, you should be able to stay outside EVERY night, constantly plowing forwards, getting as much scrap metal as possible.

Once you fully upgrade your team, start buying the big turrets. The majority of your turrets should be on the right side. You also want to upgrade your barricade twice. Once about night 14 comes around, you have to start staying in for the night. You stay on the left side and use your gun to take down all zombies, while the right side is covered in turrets. Every now and then run over to the right side to reload the turrets, covering them for a brief moment, then hurry back to the left side. If you realize that it's very easy for you on the left, then don't bother buying turrets on the left, just keep spamming them on the right.

This method will get you WAY more scrap metal than usual, will keep you safe, and will make your base overpowered. Using this method you can safely win the game without dying once. This way, you can get all the achievements in the one round, without worry.

I'm not going to insult your intelligence by explaining how to perform self-explanatory tasks, like most other guides for games do (it's ridiculous).

Problem: As mentioned, many of the achievements need to be done in one game, without dying, and without quitting the game. This applies to pretty much every achievement with a number associated with it.

Imma Take a Nap: It says you need to sleep 5 nights... obviously this means days... because you don't sleep at night in this.

Vodka: In the upgrade GUI, there's a little bottle at the top left, just to the right of "Make Guns". Just click it.

Golden Shells: This is the hardest one. Pretty much, always play as the American, and after the first few days, just constantly shoot your weapon, without stopping. I've figured it out mathematically that you need like half an hour of shooting to get to this many bullets. Also, it has to be done in one game, without dying or quitting. Just make sure you always have TONS of ammo (like over 1k). I got the 1 hour achievement BEFORE I got this, and I was pretty much constantly holding down the mouse, shooting non-stop. It's incredibly annoying, but should only take a little longer than an hour, and you need to shoot things anyways, right?

Go shoot some zombies.