If you haven't already do the Hall of Novice thing, part 7 rewards this ... http://na.finalfantasyxiv.com/lodest...m/213fc7a1359/

Leveling alt classes seems a bit harder to do without the main story to give those larger chunks of exp in between.

http://ffxiv.consolegameswiki.com/wi...ndship_Circlet (there is also another head slot exp bonus item, but stops working at 11, from the original collectors edition) is another awesome item to get if you still can. Works for all classes / jobs

Using both of those, and food for 3% bonus, and being in a FC (guild) that runs their exp buff will help you with any cross class skills you might want for your main class, as well as crafting.

Make sure you also unlock the side quest related dungeons, so you don't miss out on them....like I did lol

I'd also say, play how you like, but I did read somewhere you get a better exp bonus the higher your main class is compared to the alt class' you level.