Okay I was one of the first people to take an RP character to level 20. Since then I have perfected the leveling system. Or at least so I think. Here is my suggestion of the path to the quickest level 20 RP character.
LVL 1-5
Should be done in the starting area. To get out of the starting area, talk to the Tydin guy at the fountain in Ascalon City and take his mission.
LVL 5-8
Complete the Northern Wall Mission and get to Fort Ranik. Here take the Healer Henchman, and if you don't have good armor or take damage to quickly for her to heal you, take the Fighter Henchman. Outside of Fort Ranik in the Solo Area, you will find Bandits and others like them.
LVL 9-12
Complete Fort Ranik and Complete the Frontier Gate. Now you are at the Ruins of Sumtra. Until you are Level 10, I suggest taking the Healer Henchman. Enter the mission. You will have Prince Rurik as an Ally. He will not cut into your experience and acts as a magnificent tank. Just keep taking this mission over and over again. If you find that you don't need the healer henchman, some awesome items and gold drops here. So if you can afford to not use the henchman at this level, then I would not do so. The best thing to do is to kill everything up to the Prisons with Ascalon Prisoners in them. Then exit back to Sumtra and start again. You will want to use area spells and attacks here as they will be most effective.
LVL 12-17
Spell Casters:
Complete all Missions until you get to the Gates of Kryta. Here you will venture out of town to the North Northwestern. You may want to take a party with you the first time until you find the path and become familiar with the area. The spot you are looking for is an area exit. It is the doorway between the North Kryta Province and Scoundrels Rise. On each side of the gate you will find creatures called Mergoyles. These guys are Mesmers and have a nasty spell called Shackles which if you aren't careful will kill you quick. If you fight these guys calmly, you will be okay. The Shackles spell takes 5 points from your energy everytime you attack. But spell attacks that consume energy don't seem to be counted in as an attack. I assume warriors and rangers can fight them too so long as you use specials only. The trick here is to get right at the exit gate between the two areas. On each side there are mergoyles and when you load in to the area they all reappear ready for the slaughtering. The North Kryta Province has about 10 and the Scoundrels Rise side has 4. Until you are higher or more comfortable fighting them, I suggest just fighting the Scoundrels Rise ones. Kill the 4 then head thru the exit gate, turn around and kill them again. You can also get some AMAZING loot here. I have found upgrades for every weapon, including rare upgrades! Each Mergoyle can drop up to 60 gold as well! Again Area attacks are the key here.
Melee:
Since you couldn't do the Mergoyles, there is an alternative, though not as good. In the same area, there are Bog Skales. Lots of Bog Skales. Melee classes seem to handle these easily, but be warned they usually travel in groups of 5 with another group of 5 nearby. They can be nasty when swarming. There are lots of these in the Scoundrel's Rise area, but none near a gate unfortunately. So your leveling will be slower. If anyone can help me with a better melee approach for 12-17 please post and I will edit with your name getting credit.
LVL 17-20
You need to have gotten to the Divinity Coast point by now. Here if you exit town immediately along the path you find Ancient (tree guys will edit in a minute). They are level 17 as well and are easily soloable. They will give you 100xp each when u are lvl 17, 80xp at lvl18, 65xp at level 19 and not sure about 20 but its around 40-50. Anyways. They travel groups of three and there are about 7 groups along the road. Kill them all and then head back to town and renter. This is the Solo Area not the mission. Once again area attacks will help you survive the pounding from these trees.
PM me with any suggestions of making this guide better