If you find yourself deciding to come to Shiva then I can get you into SpiralingEmerald, granted that sack holders are online at the time.
The main area's for leveling now days is Gusgen, Garliage Citadel, Crawlers nest, Bostaunieux Oubliette and Abyssea. You need to remember you have limit break quests to do to break your level cap.
Also if you have the Destrier beret you should always wear it when leveling a job lower than 30 or if your syching to under level 30 (i.e Gusgen mines) Should help you outrun anything that chases you and if they kill you, you have auto-reraise anyway.