Diessa plateau too difficult
Try the other starting zones to level up and do events.
Diessa is 15-25 so you’re in the wrong part of the zone for your level.
The range for that zone is 15-25. What level is the story quest? If you want to level up more then I suggest doing the other starter zones and cities as well as get 100% map completion.
You can access other cities through Asura gates which are the large purple portals you see in town. Go into the charr city and the portal should be on the west side of the city. This will take you to Lion’s Arch which is a central hub for most players. You’ll enter at a section that has gates to the other cities where you can do the starter zones there.
You can go to other zones and level up some. Go to cities and discover all the points for xp. Or try another area in the zone with lower lvl mobs.
It’s not just that you’re in the wrong part of the zone. This gap happens with every 15-25 zone, at least for me, and I’ve gone through it with every race. Between the starting zones and the 15-25 zones, there’s not quite enough quest content to keep you on track. It pays off to do part of another starting zone before heading to that next area.
You’re in the wrong part of it. The area goes from lvl 15 to lvl 25. I think it’s left that is low area but it’s been a while since I’ve been through it.
(edited by Demented Sheep.1642)
It’s probably different for every play-through, and getting some levels under your belt won’t hurt. However, do check the levels of thing’s you’re going up against. If you do what I did and go to Diessa from Ashford, you’ll come out at the level 25 end and get pwned. There’s a gate directly from the Black Citadel (north edge) that will take you to the softer, friendlier, level 15 end of Diessa 
Thanks to every one of you
Yeah, go to other race zone to level up as what others had said. I have personally leveled all the 5 different races (4 races to lvl 80 and 1 race to lvl 42) in the 5 race specific zone. By far, charr zone is the most insanely difficult to quest. I got killed more time in charr low level zone in my level 80 gears than in other high level race zones. In fact, I don’t get killed that many time even in orr land.
Charr zone is just insane in my opinion.