So i returned to FF a month ago and i was in the same situation as you are now.
Try your skills and your rota at normal monsters and fates, then go on with your main story (when your not finished with Realm Reborn), i'll recommend you to buy Heavensward - the Content is not that hard, so you'll get into the mechanics and do not hesitate to get into Dungeons or Raids, the most people will help you and be nice
I had no problem getting to Level 60 with the Heavensward Content
So have fun