Methods of Leveling from most Sp to least SP:

1) Group Leves: Doing Leve Quest with 6-8 people (extremely high sp/kill leading to high sp/hr with links, you will get around 30-35k hr doing this, near 50k at higher camps)
2) Group Grind: Killing normal mobs fast for 150-400sp/kill (fast killing of mobs will net you around 25-40 k/hr depending on the level/camp/party makeup )
3) Solo Leves: Soloing your leves (will get you around 18k/hr)
4) Behest: Joining the battle wardens free leve quest basically (Great Sp until 24 then it is not that good anymore)
5) Solo Grind: Solo killing normal mobs... horrible (This is a nightmare to do... use as a last resort)
6) Quest: Like another mmo without the SP bonus (for now devs are adding it) (atm Quest are not designed for leveling, so this is the absolute worst. Designed for story line and what not)

Changing around next update though, so we will see what happens then.

I recommend getting into an active linkshell(Guild) that does things together so you can do #1 and #2 on my list easily.

This is one of the fastest game to level up in if you play with other people, it is one of the biggest nightmare grinds if you attempt to solo to cap. Not only that but getting some veteran advice will help you out immensely. This game takes awhile to figure out, having people mentor you more or less will make the game that much easier.