It does get hard to lvl around 40 but you just have to grind away. Pick up as amny Swift atk pots or something like it, Heal pots and bring as much ss as you can carry. If going solo find a area with green mobs with few people and where the mobs are not to far apart (be careful to keep track of what is agro and Social) and just grind till you run out of ss and pots or you need skills. At lvl 38 you should be able to lvl once a day ( 4-6 hours of play)
If you have a buffer /healer take white and yellow mobs. ask your Buffer /healer to care xtra ss for you so yu can stay longer.
Solo I would think the area around Giran Castle would be good
with buffer/healer go donw to Fields of Silance / Feild of whispers
There are quests for both of these areas be shure to pick them up befor you go. Giran area 1 quest Heine area 3 Quests
Best of luck to you and if you think its hard now just wait I have a Dwarf lvl 59 (lvled last night

that takes over a week (50 hours +)