Not all damage dealer classes can farm effectively in Lineage 2. This game has very different mechanics from others mmorpgs.
You can try leveling up a Orc Fighter or Dwarf as they're more tanky and deal fairly good damage.
To avoid spamming hp potions you either need to find a spot to kill mobs 3-5 levels lower than yours or/also you need a buff called Vampiric Rage, you can get it from a Shillien Oracle Lv 28+. This buff restores some hp as you hit a mob.
Avoid bosses, they'll take most of your resources in exchange of leveling fast, you don't want that. Now all you need is to explore the map and farm adena for C grade gear after you reach lv 40.