Some Suggestions for Leveling 19-25 in Lineage2
Level (Lineage 2 gold) 19-21: Do your Class Change quest. When you finish it, hunt in the Neutral Zone between the Elven and Dark Elven starter towns, or hang out in the Langk camps south of Gludin. Once you make 20, sign up with Dusk/Dawn, get a pick up group in Gludin, and poke your nose into Necropolis of Sacrifice for the first time. Do not expect too much your first time there, but make it a point to try. In later levels you're going to be spending a lot of time in Catacombs and Necropoli all over the map.
Level (Lineage money) 21-25: There are a couple of options here, but we personally only recommend one: Vanquish Remnants. Get the quest, go to Abandoned Camp, and stay right there until you make 25, then go back and turn in your badges. Try not to use shots and potions except in emergencies, and try to party with two other people near your level.
A three player party of almost any make up can tear through AC with relative ease, quickly burning through levels in Lineage2 and building up a good supply of adena and items. If you can not find a party, soloing is still possible, and downtime can be minimized if you are careful not to draw too many occurrences of multiple mobs. We have yet to find any class that cannot level consistently and make decent money doing this quest.