I am planning on getting back into FFXI soon, hopefully this weekend. My character is a level 31 RDM subbing Dark Knight. I heard that leveling in Abyssea is ridiculously easy.
How do you get to Abyssea, and are there any quests that are needed to be done in order to do so? I was soloing everything, so have grinded my way up off of kills.
Have you tried the wiki for your quest listings and mission details? That should always be your first stop.
Nobody is going to invite you to Abyssea when your highest job is 31. You can enter, but you can't contribute to the party. You need to be around level 71+ to be able to do damage to enemies and survive being hit by them. Participation below that consists of leeching (which you usually have to pay for, at a rate of 80-120k gil per hour that you want to leech for) or you running around the battlefield unlocking the Sturdy Pyxis the enemies drop, which requires you to have Forbidden Keys that your purchase with cruor. You won't have enough cruor for keys going into Abyssea, since you get it from killing enemies there, and they start out at about level 70, and increase in level as you kill them quickly. Being the person using keys is done when you already have a job you've leveled in Abyssea, and are leveling another job that way.
You don't need to be soloing to level up outside Abyssea. At level 12 you could have gone to Gusgen Mines and joined a Grounds of Valor Level Sync alliance, and that can carry you to about level 25. Then you go to Crawler's Nest for the same sort of party until level 40-something. Than Bostanieux Oubliette until 75 or 99, depending on if you use Abyssea.
Of course, leveling was explained to you there when you asked several months before...