Welcome back!

The majority of leveling is done in alliances with grounds tomes via grounds of valor:

http://ffxi.gamerescape.com/wiki/Grounds_of_Valor

http://ffxi.gamerescape.com/wiki/Grounds_Tome

Generally you'll find the first leveling spot (at least on Ragnarok) to be in Gusgen mines, page 1, right at the entrance. After that at around 34?(someone correct me if I'm wrong) we head to crawlers nest.

You'll level up fairly quickly this way, but please don't forget to take the time out to keep your skills up to date so when you get to abyssea at 75~ you'll actually be useful!

Try to find a group of people to hang out with to show you the ropes of things. If you're not dead set on your current server you're welcome to mine (Ragnarok) and my shell.

I wish you all the best!