Make sure you know what SP farming is. If you don't read up on the stickied guides in this section.
Now, I suggest indeed going with just heuksal, fire and lightning. From fire, you need the imbue, fire shield, flame body, fire protection and the passive skill. From lightning, you need: piercing force, grass walk, ghost walk ( at level 32), concentration and the passive.
Make sure you use fire imbue, not light (river fire force, not thundertiger)
Level up your soul spear skills and the ghost spear skills at level 19. Put a point into chain spear at 25 and level flying dragon at 31.
Your main moves should be;
Soul Spear
Ghost Spear
Flying Dragon.
These are absolutelly important. You might want to add some chain spear for the grind and maybe Dancing Demon spear, for it's area of effect. Oh yeah, and one more thing: don't forget the heuksal HP passive.
Hope it helps
EDIT: check this out, to know more about the skills:
http://bobtheveg.dyndns.org/SRO/Char_Build_Applet/
