Yes there's been a few on other places but this is how I got the Achievements and the forum may add to it. (post and if I like it I'll add it.) This is why I did not make it an FAQ.
Any misspells that are not on capcoms part please tell me about, And I will fix.

Zombie Genocider
TYPE: 1 Play REQ: Defeat at least 53,594 zombies.
Go to the maintenance tunnel and run zombies over by going to car to car. Another way is to go get the mantince tunnel key. Go to the white car and take laps around the U. You can take about 2 laps per car. You can save since the bathrooms are right at the door near the car. Also see This post.

Zombie Killer
TYPE: 1 Play REQ: Defeat at least 10,000 zombies.
Look up.

Hella Copter
TYPE: 1 Play REQ: Successfully repel a helicopter..
1. Go to overtime mode.
2. Get a sniper rifle.
3. Go to the clock tower in-till the cut-seen comes.
4. Go in and outside.
5. Shoot the copter with the sniper rife about 20 times.

Perfect Gunner
TYPE: 1 Play REQ: Don't miss with a machine gun.
Get the Special forces Gun and never miss with one clip.
What I did was that I went to the maintenance tunnel and went to were the butcher shop door was. Then spamed the rifle when I saw an endless sea of zombies. When I saw a gap I moved to were there was none. (note you you hit a zombie but the bullet also hit's the wall you will have to start over)

Level Max
TYPE: Total REQ: Reach Lv. 50.
Beat the game twice and you should get to level 50.
Or go do the Zombie Genocider Achievement.

Karate Champ
TYPE: 1 Play REQ: Defeat at least 1,000 zombies barehanded.
You sould be about level 40-50 to do this. Go to the maintenance tunnel and kill some zombies with 1 hit kill moves there.

Bullet Point
TYPE: 1 Play REQ: Fire at least 1,000 bullets.
Spam some guns. (Like spam 6 or 7 Special forces guns.)
Or any gun for that matter.

Snuff Shot B
TYPE: 1 Play REQ: Successfully photograph zombie Brad.
After you take out the bombs and see a cut-seen, go to the middle of the maintenance tunnel. You should see a cut-seen. Take a picture then kill brad. (You don't have to kill him but he does want you to).

Census Taker
TYPE: 1 Play REQ: Photograph at least 50 survivors.

Doesn't mean you have to save them.
Make sure you take a picture of the 10 or so people in the beginning of the game. Anyone whos alive counts.

Punisher
TYPE: 1 Play REQ: Defeat at least 10 psychopaths.
Make sure you have a decent level. And first take the missions with the psychopaths in it. Make sure you take the sniper family out. As that counts for 3 psychopaths.
I will make a guide to how to kill them later.

Psycho Collector
TYPE: 1 Play REQ: Photograph at least 10 psychopaths.
Just take a picture before the fight. As long as your going to get the Punisher Achievement this should be a peace of cake.

Carjacker
TYPE: 1 Play REQ: Steal the convicts' vehicle.
If your a high level take a katana and slash the convicts to peaces. If not take any gun you can find go on top of the picnic roof and shoot them. Then get in there car. (Make sure you Do this after 7Pm of the first day. Or the cutseen will make all of them respawn, as you have to take out the car for them to stop repsawning.

Item Smasher
TYPE: Total REQ: Break at least 100 items.
Easy achievement. Get alot of katanas and kill some zombies.
Since this is a total achievement it makes it hard not to unlock. If you want it even faster go to the supermarket and get the salmon. (breaks in two hits).

Stunt Driver
TYPE: 1 Play REQ: Jump a car at least 33 feet (10 meters).
Take the red car in the parking lot. Get some speed then jump off the top of the ramp to the mantince tunnel.

Sharp Dresser
TYPE: Total REQ: Change into at least 20 different costumes.
Go to the entrance plasa and steal some clothes.

Costume Party
TYPE: 1 Play REQ: Place novelty masks on at least 10 zombies.
Go to a toy store. Take a novelty mask put it on a zombie. Kill the zombie. Take the novelty mask repeat.

∞ Mode
TYPE: 1 Play REQ: Get the true ending.
Beat overtime mode.

Unbreakable
TYPE: 1 Play REQ: Get the ture ending without being knocked out.
Never get knocked out by the special forces or cult members.
If you do Reload or, restart the game if you saved and got knocked out.

Marathon Runner
TYPE: Total REQ: Cover a distance of 26.2 miles (42.195 km).
Just run. Should get it by overtime mode.

Stunt Rider
TYPE: 1 Play REQ: Jump a motorcycle at least 33 feet (10 meters).
Do what I said for Stunt Driver or wait in-till the motorcycle is in the north plasa and jump over stuff there.
(I hear you can do this Achievement with a bike too. )

Humanist
TYPE: 1 Play REQ: Get at least 10 survivors out of the mall.
Make sure you save people, and mange your time. You souldn't do most of the main story if your trying to save alot people.

Life Saver
TYPE: 1 Play REQ: Get at least 20 survivors out of the mall..
look up.

Overtime Mode
TYPE: 1 Play REQ: Unveil all CASES and be at the heliport at noon.
Get an A ranking by,
1.Beat all the cases.
2.At or right after 12 AM go to the hideout on the 3rd day.
3.Wait till it's 10. After a cut-seen, talk to isabella
4.Go to the helipad and wait in-till it's 12:00.

3 Day Survivor
TYPE: 1 Play REQ: Survive for at least 72 hours.
Beat 72 hour mode.

Legendary Soldier
TYPE: 1 Play REQ: Defeat at least 10 special forces soldiers.
If you have some 1-hit kill grabs use them. If not get any strong melee weapons and kill them. If your weak get some sniper rifles and shoot from afar.

Snuff Shot J
TYPE: 1 Play REQ: Successfully photograph zombie Jessie.
After you do the final case go to the security room. Take a picture of her then kill her. (Again would you want to be a zombie?).

Zombie Road
TYPE: 1 Play REQ: Walk over 33 feet (10 meters) on the backs of zombies using the Zombie Ride.
Find a packed groupe of zombiles and go around in circles on-top of there heads.

Zombie Hunter
TYPE: 1 Play REQ: Defeat at least 1,000 zombies.
Easy to do. You should get this by notime.

Peace Keeper
TYPE: 1 Play REQ: Defeat at least 5 psychopaths.
Look at Punisher.

Strike!
TYPE: 1 Play REQ: Send at least 10 zombies flying with bowling balls.
Go to wonderland plaza , and take a bowling ball from the sport store. Go to were theres a pack of zombies and use the ball.

Psycho Photo
TYPE: 1 Play REQ: Photograph at least 4 psychopaths.
Look at Punisher.

Raining Zombies
TYPE: 1 Play REQ: Knock at least 30 zombies aside with a parasol.
Go to the plaza thats outside (I forgot the name) and use the parasol.

Self Defense
TYPE: 1 Play REQ: Defeat at least 1 psychopath.
Easy to do. Just kill one.

Freefall
TYPE: 1 Play REQ: Drop from a height of at least 16 feet (5 meters).
When on the roof use the side door, and jump off the shelving unit.

Portraiture
TYPE: 1 Play REQ: Photograph at least 10 survivors.
Look at Census Taker.

The Artiste
TYPE: 1 Play REQ: Score at least 3,000 PP from a single photo.
Have the two people on the roof follow you. Once they hug take a picture.(Make sure it has a yellow PP sign).

Photojournalist
TYPE: 1 Play REQ: Score at least 1,500 PP from a single photo.
Look up.

Group Photo
TYPE: 1 Play REQ: Get 50 Target Markers with the camera.
Once the zombies come in the mall take a pitcure of a lot of them. If you don't get it there go to the roof and look down .Then take a pitcure of the zombies down there.

The following are Achievement I did not get but I think I know how.

Tour Guide
TYPE: 1 Play REQ: Escort 8 survivors at once.
Go do the above the law mission and the theater mission. and have both of the groupe follow you.

Frank the Pimp
TYPE: 1 Play REQ: Simultaneously escort 8 female survivors.
Look up but also get some more female survivors.

Full Set
TYPE: Total REQ: Collect all portraits in the NOTEBOOK.
Make sure you look around and do missions you didn't do before. Should take about 3 times of play to get all of the pictures.

Saint
TYPE: 1 Play REQ: Get at least 50 survivors out of the mall.
Don't do the main missions (or most of it) and only focus on saving people.

Gourmet
TYPE: 1 Play REQ: Eat all types of food available in the mall.
Someone or me will list a list of were and how to get the food abd shakes. Just give it time.

PP Collector
TYPE: 1 Play REQ: Photograph all PP Stickers.
I will list were the PP stickers are. Help I will be thankful for.

Transmissionary
TYPE: 1 Play REQ: Answer all calls from Otis.
You have to get all calls from Otis in one game. Meaning you have to go in every area and do all the cases.

Indoorsman
TYPE: 1 Play REQ: Spend at least 24 hours indoors.
I think you can not go outside anytime in the 24 hours. so just waste a day inside.

Outdoorsman
TYPE: 1 Play REQ: Spend at least 24 hours outdoors.
I think you can not go inside anytime in the 24 hours. so just waste a day ouside.

Clothes Horse
TYPE: Total REQ: Change into all costumes available in the mall.
Make a list of what Clothes you put on and were. Go around puting them all on in anymode.

5 Day Survivor
TYPE: 1 Play REQ: Survive for at least 5 days.
Must be in overtime mode I think. The real magaman blaster helps alot. After awhile you need to kill the bosses and mange items. I will list how much points Food gives you.
(Being level 50 helps).

7 Day Survivor
TYPE: 1 Play REQ: Survive for at least 7 days.
Look up.

Nice, my thread got a reference link!
Also, for your 1,000 bare handed kills, the grocery store is nice, too. I havent unlocked it yet (Had to run to the helicopter after about 300 kills, but to be fair I did the Genocide achievement first) but I find that having the food at hand in the grocery store is nice, and the zombies respawn in managable numbers on the far side of the store once you reach once end and you can throw a can or a cash register through the store windows so zombies will climb through faster.

what main case can u skip?

Maybe this should be a sticky, and maybe alter that Perfect Gunner hints. If your by the butcher shop anyway, if you empty the gun into a side of beef, then your done. I got it as a tip, I tried it and it worked. (Not the greatest reward, unless it has some special effect I am unaware of...but an easy goal none the less)