I'm not going to bore you to death with random information; I'm going to cut to the chase the best I know how. If you have any questions please reply and I will edit this post to make it clearer. This walk-through is to teach you how to get to level 20 as fast as humanly possible without having to take weeks to do it.
Level 1) Given to you on the training boat.
Level 2) Given to you on the Isle of Refuge
Level 3) Kill "a" goblin. (This is real tough so far isn't it?)
Level 4) You'll pick this up doing your armor quests on the Isle.
Level 5) You should be level 5 by the time you get to the Orc slayer quest on the isle.
Level 6) You should be able to accomplish level 6 (and 160+% exp) after...
Getting the 6 slot bag from the goblins on the isle
Stopping the Goblin Invaders
Completing the "talkative gnome on the beach" quest
Completing the Kill 10 sharks quest
Killing the Troll Ghost Pirate Quest
Killing Bladefin
Completing the book quest found on Bladefin
Completing any other random quests I've left out (I prefer to skip the collection quest they take up to much time)
Level 7) You should skip this level when you complete you citizen quest.
Level

You should be about 20% into level 8 when you complete the citizenship quest. You should now go online or ask your friends or high level characters of the type you'd like to be, where the trainer is. You pick up your class quest, and start working on it.
Level 9 ) You should be level 9 with about 2+% exp (in worst-case scenario) after you finish your class quest. Some classes will have even more. At this level depending on if your Freeport or Qeynos related you will need to do a little exp grinding. (Don't worry this is easy compared to higher levels)
Level 10)
Qeynos - Head outside into Antonica. Head towards the crow fields located right by the north gate. You can solo or partner up and killing the Beetles located here, that are agro to you at this level.
Freeport - Head just outside the gate into Commons, kill the critters that look like armadillos. Make sure you only fight the non-linked versions.
Level 11)
Qeynos - Stay in the fields Soloing Beetles or if you can skate your way into a group, you'll mooch some exp killing the crows in the field. (See making the ultimate group below.) (NOTE: Collect as many "Firemyst Gully" quests as you can!)
Freeport - Stay out in this area, kill these things until you don't get 1% exp for them, you might want to try your luck with the dog like critters that roam non-linked to the others. (Do not group, you don't need friends that live here.)
Level 12)
Qeynos - Stay in the fields killing scarecrows. Make your own group. (See making the ultimate group below.)(NOTE: Collect as many "A Foul Wind" quest scrolls as you can!)
Freeport - Stay out in this area, kill these things until you don't get 1% exp for them, you might want to try your luck with the dog like critters that roam non-linked to the others. (Do not group, you don't need friends that live here.)
Level 13) At this level you should be in Antonica or go to Antonica from the Commons. (I know it's not easy, as someone high level to group with you to grey out the mobs so you can get to Antonica safely.) You need a "A Foul Wind" Scroll examine it get the quest, and if you cant seem to find one keep killing crows or find out if someone in your group already has this quest. Then go do this quest.
Level 14) You should be standing outside Firemyst Gully. If you have the quest again, do it again. You can do this till level 16. If you have run out of scrolls and quests, then head back to the newbie scarecrows and kill them non-stop pulling until you get another scroll.
Level 15) You should be standing outside Firemyst Gully. If you have the quest again, do it again. You can do this till level 16. If you have run out of scrolls and quests, then head back to the newbie scarecrows and kill them non-stop pulling until you get another scroll.
Level 16) You should be standing outside Firemyst Gully. If you have the quest again, do it again. You can do this till level 16. If you have run out of scrolls and quests, then head back to the newbie scarecrows and kill them non-stop pulling until you get another.
Level 16.2-16.6) Leave Firemyst Valley and head for the Scarecrows near the Thundering Stepes Griffon station. Once again, follow the "Ultimate Group Guide" If you can accomplish the Ultimate group guide, you can pull non-stop sometimes you can even pull two double spawns, or a double spawn and a single^^ spawn. (This will be made clearer after your here for a while.) If the fields get attacked by another group or possibly even an existing group it might be necessary to pull more than once.
Level 17) Ok, keep pulling Scarecrows. DO NOT pull the bears or wolves that pass around the fields. Let the other people take care of them, so you can get the next crow spawn. They are not worth your time. Sometimes while your double pulling, other groups will attempt it too. Usually unorganized, not enough DPS, or someone is low on power groups get totally slaughtered and then break up, leaving the fields for you to clean.
Level 18) Once you hit level 18 in the Scarecrow fields near Thundering Stepes, your going to need to start you class quest. Go do it. It'll take about an hour, and you can usually solo it fairly easy. Then get back to the Scarecrow fields and follow the Ultimate Group Guide again. Typically I like to take a break before I do my quest and log for the evening or eat or something to take a break and allow my brain to rest. It's about 2 days of work thus far from the Isle, and class gaining quests you deserve it.
Level 19 ) Ok back online, getting your stuff together again. You've completed your final class quest and you need to get level 19. Back to the crow fields, follow the Ultimate Class Guide again, and blamo back in action! Levels 19 and 20 are a grind but so many people will love you and praise you for running this group because of the Ultimate Group Guide, and my walk-though. You will the shining star!
Level 20) Life is grand as you know it. Crows will no longer be good experience for any group you join. Leave the group your in, and get someone to replace you. It's time for you to start your Armor Quests (AQs)
AQ 1) Armor quests are a huge pain for everyone! Get it over with! Don't worry about debt or leveling. Get your quest for AQ 1 and just get it completed. Make jokes to cure any debt woes for other members.
AQ 2) Same steps for AQ1 you can wear your AQ1 gear now and soon your AQ2 gear.
AQ 3) This is easy to complete if you don't worry about debt. You're going to get a lot of it in Stormhold. Too many stupid players with not enough time and not everyone wants to kill your quest mobs. So jump from Stormhold to Stormhold and join another group as soon as your group splits up. Don't worry about following the Ultimate Group Guide here. It won't help. You can't wear your AQ3 at level 20, so what do you do with all this debt and gear you cant wear? - You go on to AQ4
AQ 4) Now, what do you do now that your here? This quest is a bit tougher. Play an alt, or main or whatever, play something else till you can randomly log in this character again and get a group going down here. If you can, follow the Ultimate Group Guide it will work here. I highly suggest that you attempt this during peek hours for you when you find the most players online.
AQ 5) Now this is where you go into Thundering Stepes. You want to log this character offline for TWENTY FOUR HOURS. When you log on again all your debt is gone! Yay! Now, you group up with exp groups, AQ5 groups, and complete AQ5 and possibly get level 21 or possibly 22 but hopefully 23.
AQ 6) Back to Thundering Stepes, again this time it's a bit tougher. Maybe you can, maybe you can't solo, but grab a buddy roaming around, send OOC's out for partner to kill whatever type of critters it is you need. Your going to have a tough time trying to get the "hard to find" mob like the giant Ott, or Fey Rock Heaps so your going to want to keep a watchful eye out for groups hunting the same thing. Also do some shouting and OOCing that you?re looking for the same thing.