Overview:
-Estimated achievement difficulty: 10/10
-Offline: 46 (955)
-Online: 3 (45)
-Approximate amount of time to 1000: 60-70 Hours
-Minimum number of playthroughs needed: 1
-Number of missable achievements: None!
-Glitched achievements: None!
-Do cheat codes disable achievements?: No, no cheats other than unlocking a character.

This is one hard little guy. It takes a lot of skill, and almost only Veterans can get it.

Introduction
Hello and welcome to Tony Hawk's Project 8. The game has 49 achievements, 46 being offline and 3 being online. 13 achievements are for just beating the main story, which is very hard. If you have any trouble completing a goal, just go to YouTube and type in the name for the goal. Usually it'll show you a strategy. If you're buying this just for the achievements, don't, this game is not made to pop your gamerscore up or for any ease at all.

Step #1: Getting started with Project 8.
Okay, first do the training. It's not hard and it shows you the basics. One achievement down, 48 more to go. Now, you start of in suburbia, that's where you live. Just follow the story and do some goals, indicated on your compass above. Leave the classic goal for now, those goals take skill and frustration, enjoy the game for now. Go to the gate, and you'll see a "Start here" green marker on the ground. Those are chalk challenges, you need to grind around the block there and grind to the sick marker (you can jump), if done correctly you'll achieve "First sick goal" achievement.

When you've done some goals, you'll unlock the skate park (achievement). Do some goals and get back to suburbia, you'll see a beaver at the gate. Go talk to him. Do the goal, and you're out of suburbia. (achievement) Now just go further with the story, do goals and skate around. This is the order you unlock new parts of the maps:
Skate park. (Done by now)
School.
Slum.
Factory.
Fun park.

Around the rank of 30, you'll unlock Fun Park. You need to do goals to rank up. There are also Pro Skaters, they will appear after you've gotten their phone call telling you to meet up.
Pro Skaters location:
Rodney Mullen - Skate Park
Mike Vallely - In front of capitol building. (Must get the flyer first)
Daewon Song - School.
Bob Burnquist - School, near skate park.
Ryan Sheckler - Skate Park.
Bam Margera - Slums
Nyjah & Lyn-Z - School
Williams & Dollin - Factory
P-Rod - School.
Tony Hawk - At the local skate shop. (After becoming #4, which I'll explain later)

You'll get an achievement for every Pro (except Tony Hawk), and you need to do them all for the "All Pro Challenges Completed" achievement. Oh, and keep all of your stokens, you'll get an achievement for 1000 stokens. Okay, just progress through the story and do as many goals and get in the Project 8. (Achievement - Made into Project 8)

Project 8 requirements:
AM: 50%
Pro: 25%
Sick: 10%

Step #2: Rank 4 and more goals.
Okay, you should at least have 18 achievements by now. You probably have half the gaps by now, and some secret spots. This also adds up to your rank. Getting to Rank 4 will take a lot of time, but be patient, you'll get there. Keep doing goals. Just try do every goal on Pro first, then you'll get #4 anyway. Requirements for #4:
AM:20%
Pro: 60%
Sick: 20%

Once rank 5, Tony Hawk will call you. Do his challenge and you unlock "You made it to Project 4" and "All pro Challenges completed" Now you're rank 4, try to sick every chalk challenge. They're all possible, and there is a YouTube video for every chalk goal (it'll net you an achievement too)

Step #3: Secret spots and gaps
Once rank 4, you should try to find every gap and secret spot. You probably have half of the gaps already. It adds up to your rank, so it's smarter to do it now. In the achievement guide is a good video with all the secret spots. As for the gaps, just go to YouTube and type in Project 8 [map] Gaps.

Step #4: Mop Up
As you may have noticed, there are some achievements that we haven't discussed yet. These achievements do not add to your rank or are in anyway story related. First the easy one (Which is a secret spot anyway) "Break 15 bones in one bail". Once you've unlocked factory, do the daily grind Secret Spot and you break 15 bones.

Impessing the locals - You need to get 1000 stokens, I said in the beginning that you need to keep those and not to buy anything, should almost be there by now.
"Beat a developer" and the "Play 'xx' games online". Easy, host or join a game that's active, and you'll get the achievements in roughly an hour. For beat the developer, you'll just have to win and you get it, easy.

High scores & combos: 4 achievements, need to be done in free skate. This one sounds hard getting a 1 million combo and 10 million high score, but it's quite easy.
Okay, go to slums and you have a little alley which gives you a major boost and throws you in the air. Use it, as soon as you fly away, press start and start high score run. Go out of the menu and do the nail the trick and get a good base. Now when you're still high up in the air with a 6 x 20,000 score, go out of the nail the trick and into focus. And spin around, and do no more tricks. When you land, you'll have to do a quick manual and do loads of tricks and get a huge multiplier, 10 - 15 is enough. Or if you don't want to,I don't recommend it, but use the glitch in the achievement guide.

Step #5: Ranked #1 and classic.
Getting sick on classic is hard, use the achievement guide to do it. Don't count on a first try success, it's hard and takes a couple of runs.

Now, ranked #1 is hard and not that many people have it. 1000 people in the world, 50 on this site.

The requirements:
95% sick.
5% pro.

Now the goals you should use to get the 5% pro, most of the Bail goals are just ridiculous and the system is broken. Look on YouTube, because there are some glitches that make those unbelievable stupid goals easy, and give you more of a chance getting #1. Just skip the goals you find hard, like 40 tricks on a video goal.

When you're done with that and you're rank #2, you'll get a phone call from Tony Hawk. He lets you do the Animal Chin Challenge. This is the hardest goal from all Tony Hawks together. You need to start up the building from the capital, jump off the building and have one huge combo over the whole city. You need to go through school, up to the skate park, and then to fun park. This may take up to 100 tries, it's hard.

Conclusion:
This game is the hardest game I had to complete. It's sick and almost nobody has 1000 in it. I wish everybody good luck.

[x360a would like to thank Booij for this Road Map]