Now, it is finally time to start the grind for the Elyos. When you arrive in our town in Eltnen turn in the campaign quest to Telemachus. Now from our little humble abode in Eltnen you will want to head west. Once you get out of the area surrounding Eltnen Fortress you will want to head north to the Putrid Mire.
Up here at the Putrid Mire you will find level 23 and 24 mobs. They shouldn't be that difficult for you to kill. You will want to grind here until you are level 23 or 24. The level you should leave depends on which class you are. If you're a Cleric/SM/Chanter or someone who can handle higher level mobs with ease then you'll want to leave at 23. If not, stick it out till 24.
Now from the Putrid Mire you will want to continue east into the Eiron Desert. The next best place I've found to grind is below.
Here you will find level 25 Basilisks, Kurins, Gnarls and other assorted creatures. I'd say my favorite thing about this area is guards from your town nearby patrol this road. This is a help incase any Asmodians are Rifting and try to kill you.
These mobs will take you all the way up to level 25. Now that you're done the 5 most boring levels in the game (20-25) it is time to get attunted to The Abyss and have some fun.