i suggest you aim for ligtning/fire/bicheon (bit common but effective str build)
Almost all skills in the bicheon tree are important imo (yes even the strike and smash but you can choose not to level up, same goes for sword dance, since you only need lv 1 for book 2. However i max them both for a very effective grind)
so combo's should be maxed, knock down skills should be maxed, the skill when yoou stick your blade when he's on the ground should be maxed (my favourite
) and the soul cut serie should be maxed (so on the higher levels you can kill a mob in soulcut>combo>KD or something like that)
In the fire tree max your imbue!!, don't let it a few levels behind it could be the difference of killing a mob in 3 skills or in 4. Max the passive and max all the buffs in the fire tree (except the shield buff which can be maxed later, you don't need them now)
ligtning: try to max the passive, but you don't have to it could be done later, same goes for the parry buff
try to max the grasswalk series, it makes you grind faster (imo important)
